David Buxbaum, 51, puts his clients neatly, and profitably, out of their misery. His clients are big stores, stuck with an awful lot of leftover stock at the end of a selling period or when going out of business.

Buxbaum is a liquidator. His job is to make some good of the goods which a store has overbought and undersold. And in the four years he's been at this endeavor he has matched millions of dollars of unwanted merchandise at places like Robert Hall, W. T. Grant, Kann's and Arlan's with ready willing customers.

"There's a price at which everything will sell," says Buxbaum.

He's in town doing the honors for a warehouse full of sportswear, sporting gear and shoes, the overstock of 12 Eddie Bauer stores. The sale starts this weekend at Gaithersburg in a space that until last week was four indoor tennis courts. It is touted to be valued at nearly $6 million at retail.

Marathon warehouse sales are a phenomenon of the 1970s as a greater need developed to dispose quickly of huge quantities of merchandise. And of course the profession of "liquidators" grew right along with it." In the past, of course, retailers unloaded huge quanties of merchandise, but far less flamboyantly, and usually far less quickly.

Now, with prices soaring, even the righ turn out to find items at good price.

"People will buy anything and everything, if they think they are getting a bargain," says Buxbaum. Even things they don't need, won't fit, or don't even know what they are. Like the man at a recent Robert Hall Village closing who bought two tires that did not fit his current car. "So someday I'll buy a car they might fit,"he told Buxbaum.

Another time Buxbaum auctioned off 7-foot-tall plastic display red lips "worth nothing", he says, and embarassedly stopped the auction when the bidder hit $10.

His son Paul, 23, is his partner, and often ringmaster of the circus atmosphere which sometimes prevails - announcing specials, cooking up auctions (like a recent tricycle auction, no bidders over age 10), and antics including salespersons in funny hats giving special markdowns.

Whatever the markdown, it's never quite enough for some customers. "They will often search out an excuse for an extra discount - a mssing label, a button gone," says Buxbaum, the elder, reluctantly saying a favorite trick is to "lose" a part of a coffee pot and demand a price reduction.

Paul, a former ski bum (he winces at the phrase) tells about the lady at a sale last year who demanded an additional discount since the Barbie dolls, marked down to half price, were missing their boxes. "What would you do with the boxes when you go home?" he asked. The potential customer replied haughtily, "throw them away." Said Paul - he insists, not smartly - "Well, I've just saved you the trouble." The customer got in line with the dolls and other items, but before she reached the cash register, hurled the dolls at Paul and stormed out the door.

Another customer, who hassled Paul one day each week during a four-week sale, admitted finally, that he was simply enjoying the harassment of his weekly purchases. On the final day of the sale he invited Paul to lunch in his camper. He had driven 100 miles round trip each time for the sport and now he was feting the winner.

His father remembers one customer insisting a price be put on a totally useless stick so he could buy it. It wasn't a bargain without a price tag.

Buxbaum, the elder, who wears a gold chain with two good luck charms, sports a pinky ring and a year-round tan, will deal with any kind of merchandise offered. Not long ago a bank asked him to evaluate the inventory of two growing nurseries and insisted on generic names. Buxbaum hired a local botany professor and had no problem from there on.

Buxbaum had been in the business of helping businesses grow - boosting one discount drug chain from seven to 30 successful stores in one year, and, in fact, still takes on consulting jobs in this field.

His first and most profitable liquidation was in 1974, of his own discount health food departments within stores that were going out of business. His departments were making money, but the stores were not.

Buxbaum still has a kind of health food business going on the side. He's the originator of the Playgirl diet, soybean with protein and vitamins made to taste good that started to be promoted three months ago. Son Stephen, 26, a writer, college debater, handles that end of the business.

The elder Buxbaum arrives at each new assignment with only his suitcase, scouts for a location, the fixtures, and hires a staff for the sale. Staff is always the biggest problem. "Everyday the store is open in one less day they will be employed," he says almost glumly, He writes letters of recommendations and helps them find other jobs to ease the pain of the short-term employment.

"It is far easier to start businesses than to close them," says Buxbaum, citing the limitations on time in liquidating merchandise.

For the Eddie Bauer sale, he has established the first week in July as his cutoff date.

In each city Buxbaum checks the phone book for other Buxbaums, and then calls them. That is why he expects a visit during the sales from Phyllis (the lawyer) and Martin (the writer), both from Washington and has yet to make contact with Herbert who lives in Gaithersburg. "I don't know much about my family so I never know if we're related," says Buxbaum.

He stays in close contact with one Buxbaum he in Norfolk. He's helping him get into * the National Salvage Association to pursue another project, "a revolutionary waste disposal system."

Buxbaum declares that there's hardly anything that can't be liquidated, even a pet shop, even expensive jewels. "If I could liquidate vitamin pill-making equipment, I guess I can liquidate anything."