He had a couple of problems; One is he lied, the other is that he expected the lady to back up his story.
On further thought his biggest problem is that he is stupid. He frequents a known hangout for drugs and prostitution. You need to be a little more discreet if your job is on the line.
I agree with Dallas Rain and I think he was probably using his status as APD to get a discounted rate. I not that familiar with the street walker scene but $10 for oral sex? Sounds like be was using the threat of arrest to get that rate. P