Complaints about fake branded mattresses that are a fire risk and often filthy inside have soared, leading to a public warning from councils.
The Local Government Association (LGA) is warning that the "van scam" mattresses are often simply old and discarded mattresses that have been recovered and repackaged to look like new.
Those already seized had fake fire-resistant labels, typically failed fire safety tests and were often "filthy and unhygienic" inside.
One council had reported a tenfold increase in reports of doorstep traders offering fake branded mattresses for sale.
Some sellers were even using genuine brand names on the mattresses and vans to fool people into thinking they were getting a bargain, or used the explanation that a local hotel had ordered too many and wanted to sell them on, the LGA said.
Such sellers often issued professional-looking paperwork to buyers, but this contained false or limited contact details which made it almost impossible for a consumer to get their money back under the 14-day "cooling off period".
Devon and Somerset Trading Standards Service has issued a warning to residents after it saw a tenfold increase in mattress scam complaints, from two in 2014 to 20 between January and August this year.
Dorset County Council prosecuted a trader for possessing 213 mattresses - and supplying two - which failed fire safety tests, and Enfield Council prosecuted a father and son who used false trade marks on mattresses and misleading van signage.
Simon Blackburn, chairman of the LGA's Safer and Stronger Communities Board, said: "These unscrupulous traders have no interest in the safety of the products they sell and some have now taken to selling mattresses which could create a fireball in people's homes if they catch light.
"These fly-by-night sellers don't care about the risks these mattresses pose, they just want to make a quick buck and leave you with phoney details so they can't be traced.
"Anyone offered a cheap mattress on their doorstep should not buy one. People should only buy mattresses from reputable suppliers."
Anyone with concerns over suspicious mattress sellers should call Citizens Advice on 03454 04 05 06.