Oh dear... That beats the ****ing tard of a customer I had a while ago who followed me around with a spirit level
Told him to either let me do my thing without him acting like a complete ******, or to get another
tiler. He chose the former.
Seriously, when customers do that kind of stuff, ask them who they trust more:
Some peon who can't differentiate between filled and unfilled trav, or the guy who does it for a living, every day. Atleast get a liability waiver if they persist.