There would need to be 'more lofts than people' in Britain if households were the sales' only source of goods, according to a paper from the local authorities' co-ordinating body on food and trading standards.
Most boot sales are now commercial ventures: even a small one can generate pounds 10,000 worth of business.
Among products found at sales have been dangerous appliances, unfit food, things stolen from cars and garden sheds, illegally imported duty-free goods and counterfeit toys, videos and clothes.
One council in south Wales tested 16 electrical appliances and found all were illegal.
The paper urges a requirement for traders to identify themselves and powers to seize counterfeit goods.