The prostitute says, ordinarily it's after an undercover police officer has accepted a prostitute's masturbation that he reveals his identity, so basically he's taking advantage of the prostitute, and having sex without paying for it!
鳳姐話，放蛇警員通常喺接受妓女手淫之後至表露身分，根本係佔妓女便宜，食霸王餐！