Always nice to get the occasional tip but is pretty rare. But saying that virtually all my work now is through recommendations and word of mouth. (Maybe just lucky as Cornwall is a pretty small place). I think if customers just knew that for the cost of a few biscuits and cups of tea and coffee how much more you will go above and beyond on the job. And what they will get back in return work wise will far outweigh a few quid on tea bags custard creams and boiling a kettle . The standard is always there regardless but might be a case of offering to pop back to fit accessories, seal up once 2nd fixed.. etc. Look after your tiler and he/she will look after you.