1. "You can find better prices."

Barely a weekend goes by without a flea market visit for Terry Grahl, a Detroit-based interior designer and flea-market fanatic. She shops for her nonprofit work decorating women's shelters and to add to her own vintage linen collection. But when she wants a real steal, Grahl avoids the flea market and heads to garage sales, rummage sales and thrift stores instead. "Those are the best prices you're going to get," she says. "Most people don't know the value of what they're selling."

Flea-market vendors do, which is why a 50-cent yard-sale knickknack might cost $3 or more at a market vintage stall. Grahl's recent deals include a 1920s quilt from a thrift store that she bought for $20 and guesses would have fetched upwards of $100 at a flea market. Grahl also picks up women's dress scarves for 50 cents at church rummage sales, rather than pay $15 at flea market stalls.

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Flea-market vendors say their prices are still cheaper than at specialty retailers and online auction sites. "I don't try to squeeze every dollar out of every item," says Paul Fischer, a professor of pop culture studies at Middle Tennessee State University who sells vinyl records and memorabilia at the Tennessee State Fairgrounds Flea Market. "It's still very possible for people to find something that's a real bargain." Fisher says vendors' higher prices are fair because they reflect the work it takes to find and clean up items.

Bargain hunters may find they can get the best of both worlds: Some flea markets lease stalls on a one-time basis as a garage sale alternative for sellers looking to de-clutter.

2. "This isn't 'Antiques Roadshow.'"

Forget that dream of finding the rare collectible action figure or priceless 19th century end table for ten bucks, says former Sotheby's director Patrick van der Vorst, who appraises roughly 300 items a day on his website ValueMyStuff.com. "You can tell a lot of things are picked up over the weekend at a flea market," he says. "Unfortunately, most of it really is not that valuable." What's more, shoppers aren't likely to find a real steal in a venue where most vendors are experts in their particular niche, he adds.

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Still, TV-worthy discoveries can happen, says Helaine Fendelman, president of New York-based appraisal and sales firm Helaine Fendelman & Associates. For example, collectors may find a piece that on its own isn't valuable, but when added to the buyer's now-completed set, is worth a lot. Stalls can also be so crowded that bargains go undiscovered under tables or behind other items, she says. Most surprise deals are found in unusual categories like Asian art, says van der Vorst where it's hard to distinguish between a $5 knockoff and a $5,000 original Chinese vase.

3. "Forget about one-of-a-kind finds."

Ok, so you won't get rich on your flea-market find. But most shoppers do expect a bit of originality. Not so anymore, say experts. In the era of mass-market furniture, flea markets are full of mainstream retailer leftovers from a few years ago. "It is bore-me-to-death boring to see vendors with candlesticks from Crate and Barrel," says Tim Campbell, a designer who shops flea markets all over the world. For the cash you're spending, those pieces aren't likely to retain any value down the line, he says.

Another thing to look out for: some mass-produced items may look like vintage finds. Last year, Shabby Chic introduced a line of "flea-market-inspired furnishings" with QVC, including a $42 set of fleur de lis wall hooks and a $170 hand-painted side table. "Always ask the dealer, what do you know about the piece? What can you tell me about it?" Fendelman says. That can help shoppers spot mainstream products for more accurate price comparisons.

If you're looking for more offbeat items, some regions and markets are better than others. Campbell likes the Rose Bowl Flea Market in Pasadena, Calif., and anything in Knoxville, Tenn. "There's been a lot of money that moved into those areas," which makes for a more varied selection, he says. European flea markets tend to have significantly older pieces, which yields more unique items, he adds.

4. "Good luck getting that home."

You may be on your own when it comes to moving large, heavy items like furniture. But it can be even more complicated to get purchases from flea markets abroad back home, says Campbell, who often ships from international markets. Travelers need to be aware of any U.S. import restrictions -- which prohibit purchases as varied as animal-hide drums from Haiti and gold coins from Iran -- and any export restrictions in the country where they're buying. "Some countries are very adamant about confiscating things," he says, especially if the item is an antique or could have cultural significance. Australia prohibits the exportation of some indigenous fine art, for example. Other goods may require permits. To bring wood furniture from South Africa to the U.S., for example, requires a certificate showing it has been fumigated, Campbell says.

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Travelers can avoid some potential problems by checking restrictions before they travel. Shippers can also take care of necessary documentation, says Toma Haines, chief executive of The Antiques Diva, which arranges tours of European flea markets. Many have offices on-site to handle arrangements, but you can also set up an account in advance of any shopping, she says. That way, the shipper can consolidate all purchases from different vendors and markets into one shipment.

5. "We're old-fashioned and so are our prices."

It used to be, the older the piece, the higher its price. But as the flea-market crowd shifts to younger consumers, tastes are moving more toward clean-lined furniture, funky appliances and vintage fashions from the 50s, 60s and 70s, says experts. Prices in those categories are naturally appreciating. "The young generation is not really buying antique furniture and sterling silver," says van der Vorst. The lack of buyers and ample supply from de-cluttering boomers has caused a drop in value of old-fashioned items by as much as 50%. Vendors, however, haven't necessarily lowered prices to match this drop. "Some sellers clearly didn't get the memo," says Fendelman.

Shoppers should arrive at flea markets armed with general market prices for the items from the periods they're interested in, Fendelman says. If you have a smartphone, search eBay and the web for prices on comparable items once you find something specific you like. If the item seems over-priced, consider that extra room to negotiate, she says.

Click here for the full list of Things Flea Markets Won't Tell You.