Q. DEAR BOB: My girlfriend and I both own our own houses. Next year we plan to marry and she plans to sell her house and move in with me. If she invests the proceeds from her house sale by paying down my mortgage, could she avoid capital gains tax that she would owe on the sale of her house?--Paul F.

A. DEAR PAUL: No. The best way to avoid tax when selling a principal residence is to follow the simple rules of Internal Revenue Code 121. It allows up to $250,000, or $500,000 for a married couple filing jointly, tax-free home sale profits.

To qualify, the seller must have owned and lived in the primary residence an aggregate of two years during the five years before the sale. If your girlfriend meets the two-year test, her sale profit up to $250,000 is tax-free. Paying down the mortgage on your house won't help her save taxes. For further details, she should consult a tax adviser.

DEAR BOB: I read in your column about reverse mortgage tax-free income for senior citizens. But you said both spouses must be at least 62 to qualify. I am 59 and my wife is 51. When I am 62, my wife will be 54. I don't want to wait eight additional years until my wife becomes 62, as I will then be 70. How can this aspect of reverse mortgages be handled?--Ralph M.

DEAR RALPH: If you both hold title to the home, after you become 62 the obvious solution is for your wife to quit-claim her interest in the residence to you. But she might understandably not be willing to do that unless she can be assured that if you die first, she gets the house.

This problem could be solved, after you obtain the reverse mortgage, by putting the house into a living trust with your wife named as your heir if you die first. When you turn 62 and are serious about a reverse mortgage, review the situation with a reverse-mortgage representative to determine the best solution at that time.

DEAR BOB: I have a home mortgage from a major bank. Part of the contract requires I have an escrow account for paying my property taxes. But I was recently informed they failed to pay my property taxes when they became due. I have faxed, mailed and even sent by overnight delivery the tax bill because every time I phone the lender I get a different clerk who wants another copy of my tax bill. What state or federal agency has jurisdiction so I can file a complaint? I don't want a negative credit report due to this unpaid property tax.--Joe K.

DEAR JOE: The Office of the Comptroller of the Currency regulates national banks. State-chartered banks are regulated by your state banking commission. But before filing a complaint, make one more phone call to your loan servicer and speak with a supervisor. Politely ask that supervisor which government agency regulates your loan servicer. You are entitled to the answer.

More important, your question shows you are ready to take stronger action if you don't get prompt results from the loan servicer.

DEAR BOB: I helped my son buy a home about 18 months ago. Because of his prior credit problems, the home and the mortgage are in my name. I want to add him and his wife to the title and then quit-claim my interest to them in a couple of years. He and his wife have made all of the mortgage and property tax payments. They have taken the mortgage interest and property tax deductions on their income tax returns. Are there any pitfalls in my approach?--Harlan B.

DEAR HARLAN: If your son and daughter-in-law are not now on the home's title, they are not entitled to claim the income tax deductions for mortgage interest and property taxes. Should the IRS audit them, their deductions could be denied if the IRS learns they are not legally obligated to make the mortgage and property tax payments.

From your viewpoint, are you 100 percent certain they will continue making the mortgage payments? The reason I ask is because your good name and credit are on that mortgage. If they fail to make the loan payments, perhaps because of unemployment, illness, separation or divorce, your credit could be harmed.

Your letter says you helped your son buy the home. If that means he owes you money, for security after you add him and his wife to the title, you should insist on receiving a promissory note secured by a mortgage or trust deed against the house. Consult a local real estate lawyer before changing the title.

DEAR BOB: Twelve years ago, my neighbor gave me verbal permission to landscape part of his property, which is visible from my home. I had a landscape architect design an expensive plan. Recently, my neighbor ripped out one of my plants and is now threatening to pull out all of the others. This will seriously detract from the beautiful landscaping I now enjoy. It will cost me a lot of money to relocate the plants to my property and totally change the way my yard looks. Can my neighbor do this 12 years later? Can I do something to prevent this?--Robert N.

DEAR ROBERT: Since your neighbor gave you permission to use part of his land, he can revoke that permission at any time. If you had occupied part of his property without his approval, then you might have acquired a prescriptive easement.

However, you clearly do not meet the "open, notorious and hostile" prescriptive easement requirements since your neighbor approved your landscaping of his property. The best you can do now is negotiate with your neighbor to allow your landscaping to remain. Perhaps you might emphasize how this makes his property more valuable.

If that doesn't work and if you have a lot of money to waste on legal fees, you might consult a real estate attorney about seeking an injunction to stop your neighbor from removing the landscaping. Perhaps the legal theory of "estoppel" based on your detrimental reliance shown by your large monetary expenditures might work to your benefit.

DEAR BOB: Part of the purchase contract for our home was that the seller would install a new roof. It was completed just before the title transfer. We had our professional inspector check the roof at that time. However, neither we nor our inspector noticed the roofer had used long nails on the thick eaves, which extend about two feet from the house.

The result is a couple of hundred nails protruding from underneath the eaves and tearing out chunks of wood. It looks terrible and might affect the home's value. The seller agreed to have the roofer remedy the situation, but it appears he probably won't do anything. Do we have any legal recourse or does the fact we closed the sale indicate we accepted the roofing job as satisfactory?

--Kendall R.

DEAR KENDALL: Even though the seller contracted with the roofer, most roofing jobs include a five- or 10-year transferable warranty on workmanship. If you politely ask the roofer to come back and cut off the protruding nails under the eaves, presuming that's what will solve the problem, he probably will do so.

If the roofer refuses, however, you or a lawyer might send the roofer a letter giving him 30 days to make repairs. Presuming the roofer is licensed, be sure to send a copy of your letter to the appropriate license agency.

Also, a copy should be sent to the city building department that issued the roof permit. They might refuse to issue future permits to that roofer. Should the roofer still refuse to fix the problem, you could hire someone to do the job and then sue the roofer in small claims court for the cost.

Your situation shows why it isn't always a smart idea to let the home seller handle repairs just before the sale is ready to close. Instead, if you had accepted a credit for the roof cost, then you could have selected the roofer and had better control over the quality of roofing work.

DEAR BOB: Thank you for your advice to make a low down payment on a home purchase. When we bought our first home about a year ago, we heeded that advice and made only a 3 percent down payment. About 10 months later my husband's job was eliminated and we had to move.

The mortgage lender allowed a friend with good credit to buy our house and to take over our mortgage payments. Since the home had not gone up in value and since we didn't have big equity tied up, we came out much better than if we had to get a buyer to make a big down payment. In November, we bought another new home for a low down payment, too.--Joyce R.

DEAR JOYCE: As you discovered, buying a home with the maximum mortgage available makes sense for many reasons. That's why I recommend home buyers conserve their cash and leverage their home purchases so they don't tie up big equity in a house, which might be difficult to sell on short notice.

Readers with questions should write Robert J. Bruss at P.O. Box 280038, San Francisco, Calif. 94128.