UK regulators are taking enforcement action against unnamed online gambling firms which they suspect of breaking consumer law.
It is part of a crack-down by the Competition and Markets Authority (CMA) on misleading promotions and obstacles to claiming winnings.
Many readers have got in touch with the BBC about their experiences using betting websites.
Here are some of their stories:
Matt, County Down
Matt told us that when he was playing live casino roulette, he deposited £10 and then a pop-up appeared on screen offering him a further £10 as a matched bonus, which he accepted. Under the rules of the game he now had a £20 bonus but no cash.
He won £300 but when he wanted to stop playing his balance showed up as empty. His bonus fund, meanwhile, had £300 in it, but he was not allowed to withdraw that.
He rang the company which told him that accepting the bonus "locked my initial deposit in with my bonus £10".
Under the firm's wagering requirements the £20 bonus funds had to be staked 50 times - or £1,000 - before he could withdraw any winnings.
On that occasion he won £280 but that was the only time in about five years of online betting that he had won anything when wagering requirements were in place.
Robert, County Durham
Robert wrote: "I've repeatedly won large amounts of cash only to be stalled when trying to withdraw. Often the site claims it needs to run a verification process which takes days to complete and requires photos of the method of deposit and proof of address.
"These aren't performed prior to depositing. Other sites deliberately take days to transfer cash and allow you to cancel the transaction at any time.
"I now only gamble on specific sites that can be trusted to withdraw cash quickly."
Robert also said he would not now take any of the welcome offers because of the wagering requirements. However, he pointed out, some sites automatically apply the promotions and then punters have to contact the firms to get them removed.
Daniel got a £20 bonus when he bet £10. He won £790 but the online site refused to let him withdraw the winnings because it said he had not met the wagering requirements attached to promotion.
The firm then "banned my account, nothing I could do about it", he wrote. "Unscrupulous online betting sites have created a bad name for the business.
Claire Fleming from Realbookies.com said: "We would urge online betting customers to do their due diligence before using sites - read the terms and conditions, check out the 'about us' sections to find out how the business works and look up testimonials of others who have used the site.
"This way people who want the convenience of online betting can be sure they are using a well-established and trusted site."