I am a fabricator. Tough problem. If the countertop was properly installed there is no mechanical stress on the granite and no reason for it to crack so the too tight faucet nut is at least possible. I would look along the underside of the countertop to see if it is shimmed so that every part has support. Typically the tops of the cabinetry are not perfectly level and the underside of the stone is also not perfectly flat so some shimming is required. if some section is not supported then a crack developing is quite possible. However, since granite has a compressive strength similar to concrete it's difficult to imagine tightening a faucet nut enough to harm the granite. In fact, it seems impossible to me. unless you can determine that the tops were improperly installed your best bet is to let the fabricator repair the crack. A well done repair will make the crack invisible or nearly so. you might ask the fabricator if the sink area is "rodded". Rodding is the technique used to strengthen the rails around the sink by glueing in a steel or fiberglass rod in the underside of the rail. the rod prevents movement much like rebar in concrete in the event a crack develops. A repair of the crack is much more likely to be permenant if the stone is rodded.

As I said, the appearance doesn't so much bother me as much as the unevenness and gritty feel do. Will the material used in filling the seam wear out over time?

These are my pics of my countertops placed Friday June 22, 2018. I cried looking at these seams. It looks so cheap. Fabricator explains that's the way it comes. I explained that I shouldn't be able to see the seams so clearly. It looks so unprofessional. They ended up taking them back to their warehouse. In hopes they say if it is quality control will try and fix it just to make it look better. Otherwise I will have to pay an additional fee for them to come out again to install. I just don't know what to do and if still looks the same. This is the first time I've replaced my counters in 24 years. I don't and can't live with it. looking at this for another 24 years. It looks so cheap and it really was not it's a lot of money to me. I hope fingers crossed that they will fix this problem. They never told me that there would be such seams. I thought the edges were done by a machine and it would be all one piece. I have read up on this and now understand there are seams. But now I do know that they should not look like this. If they are good fabricator you shouldn't be able to see them so clearly. I will find out next week what happens.

Seeing this in 2024 and that seam is TERRIBLE! Either the technology has completely improved or people saying it’s completely fine just have a very low standard. 😳I have never signed off a counter with seems like this, nor will I.