All legitimate sites will have licences from the gambling regulating authorities - such as from the UK or Malta. They work hard to comply with their guidelines and gain these licences. Online gambling is an extrememly competitive industry, and they all want to meet the standards. The regulators are very stringent with their requirements. Check at the bottom of the home page of each site. They should have at least one licence listed there, if not more, so you can know that they are legitimate.