DEAR BOB: In August 1985, we finally sold our town house condominium. It had been listed for sale with three Realtors but none had been able to sell it because of a glut of town houses and condos for sale at that time. The buyer was an investor who made a $3,000 down payment, which the Realtor agreed to take as her discounted sales commission. We got nothing out of the sale. The investor took over our assumable VA mortgage and gave us a $4,500 second mortgage for our equity. He immediately rented the town house for $550 per month and never made a mortgage payment to the VA or to us. The VA waited about 12 months before foreclosing. There were no bidders at the VA auction sale so the VA now owns the town house, wiping out our second mortgage. To make matters worse, the VA notified us if they suffer any loss, we will have to pay the deficiency. The buyer seems to have left town as nobody can find him. What should we do? -- Ava H.

DEAR AVA: Unfortunately, you were a victim of an equity skimmer. If he didn't make any mortgage payments and collected $550 monthly rent for a year, he pocketed $6,600 at your expense. You could have prevented him from milking the property by promptly foreclosing on your second mortgage, regaining possession and reinstating the VA first mortgage.

However, you still might be able to negotiate with the VA lender to buy back the town house for the amount owed on the mortgage. This would avoid the probability of the VA suing you for a deficiency loss.

Your situation shows why home sellers whose buyers take over a VA or FHA mortgage should insist on being released by VA or FHA of further liability on that old mortgage. For further details, consult a real estate attorney.

DEAR BOB: We are shopping for a mortgage to refinance our home. Since the cost of a fixed-rate mortgage seems too high, we are considering an adjustable rate mortgage. One S&L we talked to has a ''convertible'' adjustable rate mortgage where the loan can be converted into a fixed-rate loan anytime during the first five years. It looks like a good deal to me except we would have to pay a 1 percent conversion fee. Are there any other pitfalls of these convertible loans? -- Ryan W.

DEAR RYAN: You are correct that the convertible adjustable rate mortgages are a good deal for the borrower. These new loans, which have just come on the scene in the last few months since Fannie Mae began buying them in the secondary mortgage market, give borrowers the hope fixed interest rates might drop in the next few years.

In addition to the loan fee cost of conversion, another possible drawback is that some of these loans are convertible to a fixed interest rate only during a limited time period. The best loans are convertible at any time. But some are converted at an interest rate that is higher than the lender's rate for new fixed-rate loans; that hardly seems fair.

As with any loan, shop carefully among at least a half dozen lenders to find the best terms.

DEAR BOB: Several years ago, we bought a small gift shop and building for $65,000 in the busy historic district of our city. We have lost money on the shop and I have had two major surgeries for cancer, which seems corrected. For the last three years, this shop has been our home. Now we want to sell it and build a home. Please comment on how we can sell, use the $125,000 home tax sale exemption as I am over 65, and avoid tax. Several people tell us our property is now worth about $250,000. What should we do? -- Mr. C.B.

DEAR MR. C.B.: Although your gift shop hasn't done well, I'm glad you have a substantial profit on the value of the building. Your situation shows why most investors do much better with real estate than by going into business.

Your first step should be to get one or two professional appraisals of your building. Be sure the appraisers have experience with commercial properties. Although it is no guarantee of competence, an appraiser with the professional designation MAI (Member, Appraisal Institute) has the best credentials.

Next, talk with nearby property owners. Perhaps one wants to buy more property in the vicinity. If not, then list your property with your town's best and busiest commercial real estate brokerage.

For income tax purposes, you will be making two sales. One is the value of your personal residence portion of the building. The once-per-lifetime $125,000 ''over 55 rule'' tax exemption applies if you have owned and lived in the residence any three of the five years before the sale. But your profit on the commercial portion's sale will be taxed as a long-term capital gain. Consult your tax adviser for full details.

DEAR BOB: As a real estate agent for 12 years, I especially enjoyed your recent article explaining the problems in the real estate appraisal industry. I fully agree there should be some form of education and licensing requirements to weed out the inexperienced and incompetent appraisers. My speciality is selling luxury homes, so I'm constantly arguing with lender's appraisers who value a house for less than the sales price. But a recent problem that has developed on two of my listings is that the owners hired inexperienced appraisers who estimated the home's market values higher than what I and other local real estate agents can get buyers to pay. Although I took these listings at the appraised prices, the homes haven't sold. I asked the sellers to reduce the asking prices, but they point to their so-called professional appraisals and talk to me as if I don't know what I'm doing. Your advice please. -- Sophie R.

DEAR SOPHIE: As you know, an appraisal is an estimate of a property's market value, usually based on recent sales prices of nearby comparable properties. Until a home sells, a professional appraisal is the best guess of its market value.

Appraising tract or subdivision homes is relatively easy because most of the homes are similar so they are worth about the same, of course adding or subtracting for special features and drawbacks of each home.

But appraising luxury higher-priced homes is much more difficult. For example, recently, two appraisers estimated a $50,000 difference in the market value of my home. During a ''rising market'' in a neighborhood without many home sales, one appraiser was using sales price data as much as six months old, whereas the other used more current data. Naturally, I insisted the low appraisal be redone. On the second try, the appraiser increased his appraisal by $35,000.

Appraisers get mad at me when I suggest the real estate agent accompany the appraiser to provide information on the home being appraised. But agents often have more current data on comparable sales than do the appraisers.

When an appraisal is higher than you think is correct, I suggest you contact the appraiser and ask for an updated reappraisal. Most appraisers charge a greatly reduced fee for supplying more recent comparable sales information to redo the original appraisal. Perhaps this will help get your sellers to reduce their asking prices.

I'm certain you are aware if a home is very expensive or if the local home sales market is glutted with listings, the property may take six to 12 months to sell because the number of potential buyers is so limited. Your sellers should be counseled to consider this reality. Of course, your efforts for high priced listings must be adapted to the market, such as printing and distributing color brochures rather than just using newspaper ads and the multiple listing service book to get the home sold.

DEAR BOB: We recently listed our home for sale. After the listing was signed, the agent almost immediately took a for-sale sign from the trunk of her car and put a ''lock box'' on our front door. She put the key we gave her inside the lock box. Although we presumed the agent would put a sign on our lawn, the lock box was never discussed. The agent says it lets other agents easily show our home if we are away. But I am concerned about an agent coming into our home unannounced. Although we temporarily agreed to leave the lock box, we are having second thoughts. What do you recommend? -- Ginger T.

DEAR GINGER: There is no easy right or wrong answer to your question. Real estate agents agree a lock box makes a home easy to show to prospective buyers. Although most agents will phone you before showing your home, unfortunately, a few impolite agents will show up without phoning first. To prevent surprise visitors when you are at home, perhaps taking a shower, be sure to lock the door from the inside with a chain or dead bolt.

While your home is listed for sale, never leave valuables around. Either store them in a safe deposit box or hide them away safely. There have been a very few cases where a real estate agent or their client used a lock box to gain entry and steal valuables while the owner wasn't home. But the advantage of making your home easily showable usually outweighs this slight risk.

DEAR BOB: In a recent column, you suggested to a condo owner concerned about the owner/renter ratio in his condominium complex that the owner's association restrict new rentals so the absentee owners will eventually be forced to sell to owner occupants. I am very interested in this problem because I live in a condo and am on the board of directors of a complex that is rapidly approaching 30 percent renters. Are you aware of any condos where the by-laws totally prohibit rentals? Where can I get more information? -- Susan N.

DEAR SUSAN: My mother lives in a 44-unit condo in Minneapolis where rentals over one year are prohibited. The excellent result is rising market values in her building during a generally sluggish condo resale market.

For further information on the legal aspects of what other condo associations have done about the ''rental problem,'' I suggest your association join the Community Associations Institute. Write to James Dowden, 1423 Powhatan St., Suite 7, Alexandria, Va. 22314 for details.

Readers with questions should write Bruss directly at P.O. Box 6710, San Francisco, Calif. 94101.