" ... My point is they aren't returning phone calls and they have the money. There is zero that can be done if they don't care enough to do the job correctly in the first place and won't answer the phone now. The time to do due diligence was well before now." While I do agree that the job should have been done correctly the first time, there is a possibility that the OP can still get resolution and maybe it's not time to throw in the towel just yet. A recent poster just went through some quality issues with a low-cost pre-fab company and they refunded her money, so resolution is not impossible. The OP posted on Saturday, so maybe the shop is closed for the weekend. And as adreak100 suggested, the OP's CC company or bank may be able to assist. " ... Lowest price fabricator that you could find? Or double the price of that guy? If the first, you got what you paid for. The second, you wouldn't have even had to make the call because the problem wouldn't exist." Maybe the OP was working in a very strict budget. It doesn't mean they shouldn't get a decent job where the gap can at least be covered by the backsplash of their choice. It's not really fair to say that everyone who doesn't pay the highest price deserves to get ripped off. Just MHO. " ... They don't get to blame the wall; it's as irrelevant as what they had for breakfast." LOL.

I would say the standard is "no gap" that is visible to the eye. If there is gap due to defect of the wall (it is not square), then the countertop should have been cut to accommodate that. I would not be comfortable with caulking of that size. Only other way to mitigate it is to have a backsplash made out of the same countertop material. that way, it would be thick enough to cover the gap, but have something to support it other than the caulking.

I am buying new construction and they have had an issue where they had to remove and rehang the cabinets and countertops. after they finally reinstalled everything, I see a gap between the walls of one of the slabs of quartz. The other slab is tightly flush against the wall. what bothers me is this is the part nearest to the sink. is this acceptable?

If the gap is consistent across the back and not caused by uneven walls, then the installer just needs to push the countertop farther back to the wall, unless there is something about the cabinets that prevents it from going back another half inch. As to how that can happen with a professional company, not all are at the same level. If they are used to always doing the 3-4 inch matching backsplash, they get used to taking shortcuts, because those matching backsplashes hide all the sins of the countertop meeting the wall.