You would need to check if, subfloor restoration is part of your quote before disputing.

@G & S Floor Service the quote was for an entire remodel which included the flooring. I assume the quote was to have flooring be done properly. What I'm trying to figure out is whether or not flooring should be on a level surface or if that can create problems with flooring down the road (he's trying to make me sign off on any issues that may arise) and/or kitchen issues from sitting on an unlevel floor.

Flooring needs to be flat, not necessarily leveled. Tolerance for flatness is 3/16" flat over a 10 feet span for wood floors. Your floor can be pitched 4" and still be flat. It would still be acceptable. Cabinets on the other hand, needs to be leveled.

A dip or sag in the floor starts at the joists which can have a number of causes, the correction of which is sometimes a structural one, starting in the basement. If it is a "significant dip" that's not necessarily something you can correct by "making the subfloor level". I lived in one house with significantly sagging floors which definitely affected what the height of the toekicks were along the bottoms of the leveled cabinets and what the mouldings looked like at the top of the cabinets. That house was 170+ years old. I currently live in a 50+ year old house house with a distinct sag in the middle because of the way the staircases were framed. We corrected that partially and it involved jacking the joists up in the basement and adding some posts in the basement. How much work and expense do you want to get the floors level? That's your call, really.

Thanks everyone, very helpful! I think I've got my answers :)