Fakes doubling as big brands like Beats by Dr Dre headphones are being sold on Facebook by cheats aiming to avoid detection.
Lincolnshire Trading Standards are warning shoppers to steer clear of offers that seem too good to be true – because they probably are.
And some goods, like fake GHD hair straighteners, could cause injuries or spark fires.
Trading Standards service manager Mark Keal said counterfeit goods used to be sold on eBay but the cheats are turning to Facebook because “it’s a little bit more smoke and mirrors”.
Visitors to people’s Facebook pages have to be accepted as “friends”, making it tougher for the authorities to keep an eye on what’s going on.
But Mr Keal said: “There are ways round it and we do investigate sellers who are selling in that way.
“We are starting to have some success at stamping it out but it’s a new one for us.”
Trading Standards are particularly concerned about counterfeit electrical goods, like the fake GHD straighteners.
Mr Keal said the straighteners heat up more than the real product and there have been incidents elsewhere in the country of users being burned and fires being started.