Every reputable poker site has a dedicated procedure for handling complaints and allegations of wrongdoing or collusion).
Just contact the site with your complaint as the good rooms will have dedicated departments to investigate cases of possible collusion or cheating.
Sites are also good at spotting multi-accounting, the process where disreputable players log on to a site using multiple servers and accounts. This is a form of cheating that, while not common, has led to some high-profile cases in recent years. In almost all cases, multi-accounting is caught and dealt with.
Security - Keeping the game fair We operate online poker cash games and tournaments, taking a small amount from most cash game pots (in the form of ‘rake’) or tournament buy-ins (via entry fees) as financial recompense. Operating with this business model, the integrity of the game is paramount to our success. Bovada’s online poker security uses tried-and-true encryption methods. The same systems used by most online banking systems. The same systems used by most online banking systems. We stick to the highest standards of personal information protection, internally, in all transactions, and on our poker software.
And to protect you against players who shouldn't be on the site (banned players or under-age), ID verification is usually practised by solid rooms. When you make a real-money deposit, you will be required on some sites to scan in photo ID like a passport or driver's license and send it to your site. Once approved, you will be free to play for real-money on the site. While a pain, age and ID verification is essential for a secure poker experience.