A traveling buyer of collectibles is in Pittsburgh this week offering "instant cash" for rare coins, jewelry, gem stones, guns, historical documents and other valuables.

But before you head over to the event hoping to get top dollar for grandma's prized silver tea set or grandpap's beloved pocket watch, experts advise doing your homework. They say you should have a good idea of what your valuables are worth before showing up at such events or you risk getting taken.

"Companies that do business like this, setting up in hotels and keep constantly moving, are notorious for paying way below the market value for what you bring in," said David Sklow, researcher at the American Numismatic Association, the country's largest trade association for coin collectors and dealers.

"Make yourself aware of what you have so you aren't going in there blind," Mr, Sklow said, adding that taking your collectibles to a buyer's show isn't the place for an unbiased appraisal.

Experts suggest getting multiple estimates from local reputable dealers or appraisers. In the case of valuing coins, reference books -- available at libraries, in book stores or through the numismatic association -- should be an additional resource, Mr. Sklow said.

The operator of this week's event, being held at the Holiday Inn on McKnight Road, said yesterday that accusations that companies like his prey on the uninformed are unfounded.

"People who don't have an appraisal or knowledge of what they have, no matter what you offer them, they are not sellers," said Todd Tyre of Tyre, Bailey, Roberts & Associates.

"We want people to shop around because we find those people are so much easier to deal with than people who are uninformed."

He said the assertion that companies like his don't make fair offers is unfair. "That's a statement that is not very thought out. It doesn't apply to me or our company," he said.

Mr. Tyre said his company held a collectibles event in Pittsburgh last year at the Holiday Inn in Green Tree and "had no complaints" from consumers.

But experts said consumers should think twice about doing business with a company that leaves town after a few days because there will be nowhere to turn if problems arise.

Mr. Tyre, who said his business is based in Cincinnati, Ohio, said he gives customers a toll-free number to call with complaints.

"Occasionally there have been people who leave messages on the 800 number," he said. "There have been items people have sold inadvertently and wanted it back. A lot of times we've been able to retrieve it and send it back."

Warren King, president of the Better Business Bureau of Western Pennsylvania, said there have been no complaints lodged against Tyre, Bailey, Roberts in Cincinnati, which is where any complaints nationwide would be forwarded.

Still, he advised consumers to be cautious. People who don't bother to check the appraised value of their collectibles won't "know any better" if they are offered a bad deal, he said.