Terms for hiring a contractor to do some work?

[Jack B.]

I have a bathtub leak in one of my upstairs bathrooms. It requires someone to go into the drywall downstairs to fix. The previous owner tried it themselves and didn't resolve the problem, like pretty much everything else he tried to do himself.

Anyways, he gave me a quote but in the quote the terms are that once he opens the drywall, if there are additional issues that will increase the cost, he will discuss them with me before proceeding. Yet there is no cap on dollar amount such as a "not to exceed $200 in additional charges". I'm curious, should I not ask him to add that in there? Is his verbiage standard for residential contractors? Is there another way to have him word it?