No, it's not common but it does happen. I NEVER do. It's not a dating app or a hook up. You're buying a service from him, and if he isn't "up for the job", then he shouldn't be in the business. (no pun intended) I do always describe myself in detail, age, looks, body shape, cock size, likes and dislikes.
I have no problem with a provider that looks at porn or closes his eye and fantasizes about whatever to be able to perform and get himself off.