I'm a longarmer and I would never expect a tip. A couple of clients have given me some extra once or twice - I'm trying to get over that making me uncomfortable and to accept it gracefully. But I'd never expect them to do it every time.
My mother once said to me (and maybe this is really bad advice, but it's stuck with me) that she doesn't tip her hairdresser when she goes to someone who's working for themself, or to the salon owner. They charge the rate they want to get. If they are working for someone else in a salon, a tip is appropriate, because they are only getting a portion of what the hair cut cost. So, since a longarmer is working for themself, I would not tip.