Agree with others that you shouldn't over think this. I think I'm fairly realistic about where I am on the attractiveness scale. Sometimes I get compliments, sometimes I don't. But, for me, I think I want to think they are enjoying themselves with me. As Manhattan correctly says, good providers will seem to enjoy themselves whether they do or don't. But one of my regular provides, now that we're 5-6 times in, has first started climbing on the table at the end to cuddle with me, usually going over our time, and has recently kissed me, which he hadn't done before. This makes me feel like he really does enjoy being with me, which is the most I could hope for.
*edited to add the point I forgot to make: actions speak louder than words. I think you can tell if a provider enjoys being with you.