Shoppers are being warned about the danger of liquidation sales, bankrupt stock disposals and mock auctions.
Brighton and Hove City Council has received complaints from people, including a shopper who paid £60 for a camera which turned out to be an empty box.
Trading standards manager John Peerless said goods in genuine sales were priced up but in mock auctions they were often left unpriced on a stage.
Auctioneers started with genuine bargains but the real money was made later, often when customers were under pressure, said Mr Peerless.
He said: "It is often difficult, if not impossible, to get your money back if the goods are faulty.
"People who seem to be getting bargains are often phoney customers planted in the crowd.
"We advise people to think very carefully before going to these sales."
He warned people to make sure they did not get caught up in the excitement and not to bid for unknown items in one lot.
Goods should always be examined before people left sales and no one should sign blank cheques.
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