I haven't had a trial yet, but I think the general rule is if the money is going directly to the person doing the service (make-up, photography, etc) then a tip is not required. But if you're getting a service from someone who works for a company and isn't independent, then you should tip. I hope that makes sense!
As a side note, my photographer (who is independent/owns the company) put in her FAQ - 'Do we need to tip you?' - No, but the size of your reprint order is an indication of your satisfaction with us. Recommending us to others is the greatest compliment. (not exact words)
