I'll list three situations. This is long, but I've actually been thinking about this lately.
1. Guy I met on Match.com contacted me to 'hang out' for the night at my place. I replied, "I feel something will be expected." Not because I was prude, but because 1. I may not wanna' do it with him, 2. I was an escort at that time and felt he would be upset if he found out he had sex with a pro. Now, we ended up jamming together, (we are both musicians,) and we hit it off... here's the point. I actually thought, "Jeez, I enjoy f***ing hobbyists MUCH more than this!" To be quite honest, the skills here are more consistent.
Afterwards I did think "I just wasted my va-jay-jay on some dude when I should be saving it for work!" How f***ed up, lol.
2. A guy I met on Match last November before I ever even considered this... kept asking via text when I was going to come into town. I dodged the texts, but then agreed. Much chemistry on my side there. He seems only to want a date every couple months so I felt I wouldn't be hurting him.
As "it" was about to happen, I excused myself to pay for more parking... then called my pro friend panicking, asking her if I should tell him first. She said, "Hell no!" (In a more mature way, of course.) "You can't just tell that to anyone." After 15 minutes of counseling and helping me with that and the fact that I felt I had to 'perform' rather than just enjoy the experience, (after all, I didn't have to worry about reviews in my head in this case,) I went back up. We were just hanging and touching at that point, but he would have taken sex any time. After calming down a bit, my inner passionate demons emerged and I seduced the hell outta him and we had mind blowing sex. I left feeling attached, but quickly de-tached after my first client... ahhh, back to the norm.
3. I met a guy for a 'hook up' on CL a few months back. THE most GORGEOUS thing I've ever touched, let alone talked to in my life. Amazing sex every time, again, before I started this. I was around my home city on tour a couple weeks ago, bored one night after work, and shot him a text to say "hi". After confirming he was a-go for a visit, I did tell him what was going on... as I knew this guy wouldn't judge me. I went over expecting to give even better sex than before, and expected to get the amazing relief I had with guy #2. Not so. I left evaluating my every move, embarrassed I didn't "do" better now that he knew what I do. I left kinda' short changing myself instead of what used to be... "Man, that was HOT!" Probably won't do that again.
So... I'm always evaluating my performance instead of just enjoying hot passionate sex on regular encounters... could be guilt, could be the fact that sex this way has become the norm to me.