Thats about it, if you have seen them in lots of lobbies, played them and noted that their good, or sharkscoped them and seen that their good. There is no intuition that will just tell you if someone is a reg.

AP/UB have a long long history of scandal and inaccurate responses to security leaks and outright cheating.A new company recently bought them, but I recall reading at least 6 months ago that the goal of the previous company was just to run up a ton of debt and then sell the company for nothing to another holding or something along those lines.The new people should be thoroughly looked at before you decide to play there.  We still offer rakeback there, but more of a response to the players that like the fishy playerbase than an approval of the way they have done business.

There is a difference between the word "reg" though, because there are both good and bad regs.  If they have good stats (esp ROI) and a lot of games played, that is a good way to draw the line between good/bad.