It depends a bit on how long the sit is. I clean before so a one week sit, meh - I just tell them to clean after themselves (such as wiping up spills and crumbs). I would clean the guest bath anyway when we got home.
For longer sits I just tell sitters to do maintenance cleaning. Never had any major issues. Sometimes there is something forgotten, eg forgot to take out trash or left some mugs in the sink. No biggie.