Oh my gosh, this is the third time I have responded. You would think I lived near where the shop might open! (I don't.)
If you offer classes, have a strict policy of, "No food or drinks, except bottled and capped PLAIN WATER on the work tables." I once had a woman spill her coke on some of my things, and all I got was an, "OOPS!" from her. If people want to eat or drink things that can stain, it should not be done at the work tables.