The biggest overhaul of consumer protection laws in 40 years has come into force.
The new Consumer Protection Regulations will ban 31 types of unfair sales practices outright and tighten controls on traders ranging from double-glazing salesmen to fortune tellers.
The changes adopt an EU directive requiring all businesses to treat customers fairly, closing loopholes that rogue traders have previously been able to exploit.
The Office of Fair Trading (OFT) and Trading Standards will enforce the new rules.
Businesses breaking the law face substantial fines and prison sentences, depending on the seriousness of the offending.
The regulations outlaw traders using misleading statements, fake credentials and aggressive sales practices.
Among the tactics that are now illegal are bogus closing down sales, limited time offers that are later extended, false testimonials on websites and high pressure sales techniques, especially those likely to harm the elderly or vulnerable.
Fortune-tellers, astrologists and other mediums are among those opposing the new laws, saying they will be forced to tell customers that they are offering "entertainment only" and their work is not "experimentally proven".
Consumer Affairs Minister Gareth Thomas said: "Honest traders understand the value of treating customers fairly and they've had enough of losing profit to the small minority of rogues who use underhand tactics to get ahead.
"The Consumer Protection Regulations will deliver better protection for consumers, cut red tape and put in place a simpler and clearer consumer law that will be easier to interpret and enforce."
