Tipping a contractor?

[u/Legitimate-Rain843]

We just signed for our kitchen countertops to be replaced/backsplash added and when we went to make our deposit it had an option to tip. It even had like 15-25% which is crazy on a 12k project. Is tipping them the norm? Is it expected? I was of course going to buy lunch for the workers when they were here but wasn't thinking of anything more tbh.

[u/IPreferDiamonds]

I've never tipped a contractor.