Some thoughts about picking a fabricator (stone or quartz)
I am a fabricator.
Unfortunately there seems to be more variation from the best to worst companies in the stone fabrication business. Here are some suggestions that might help picking a fabricator.
In general, a recommendation from a contractor or cabinet shop should get strong consideration. The contractor or cabinet shop represents repeat business for the fabricator so they have have more leverage in the event of a problem and they also won't keep a fabricator that consistently does a poor job. In my area a cabinet shop or contractor mark-up is 10-15% over a wholesale price. Typically the price thru the 3rd party will be a little higher that what you might get direct.
Kitchen and bath stores generally have much higher mark-ups but again they have the advantage of being repeat customers.
Designers can offer a lot of value BUT I've had many experiences where they recommend a material that is unsuitable for the application or they provide designs that are not readily manufacturable with stone. This puts the homeowner in the unenviable position of trying to figure out who to listen to; the designer they're paying a lot of money or the stone guy.
A good look at a fabricators showroom can give you some indication of the quality of their work.
Look at their polished edges from several angles. If you can see prominent horizontal lines in the edge thats an indication of a shop that is putting out "production shop" quality. Not bad, and possibly cheaper, but no where near state of the art. (Even with a CNC polish good edges are possible but it takes more skill, more time, and still leaves the horizontal lines; just much less conspicious ones)
Look at their sink cutouts. Again, horizontal lines are a negative. Ask them if you'll have a reveal, overhang, or your option.
Look at their seams. Most of the time a seam should be practically invisible; no thicker than a razor blade. It should be most noticeable because of the grain transition. Some stones, which are "chippy", may have a slightly wider seam. A good fabricator will discuss such issues with you during the stone selection process.
Look at the caulking in their showroom between the counter underside and cabinet and splash to wall. The caulk should be minimal, straight edges, and NO smears. A 1st rate caulk jbs takes time and a commitment to quality.
Look at edge samples in the showroom and, specifically, any laminate samples. A 1st rate laminate has a seam that is practically invisible. Most fabricators don't do the extra work to get a hairline seam on laminate.
If you can ask to see an actual install. Some fabricators do better work in their showroom than in peoples houses.
There are 2 kinds of shops in the industry. Production shops, which put out a finished product that is generally deemed acceptable. Production shop edges will be full of horizontal lines characteristic of a CNC polish and they typically do not provide the one on one time with the customer during the stone selection process. Many people are satisfied with this type of service. High volume quartz countertop suppliers are often production shops because the material is virtually the same regardless of color and they don't have the layout considerations associated with the movement available in many natural stone colors.
"Craftsman" type shops are much more focused on quality and customer service. Some large volume fabricators manage to maintain a craftsmanship style business but more typically such a shop would have a max of 20 -30 employees.
A good fabricator will help you pick your slabs. He or she will see things in a slab you won't and also mention fabrication issues which might arise with a particular stone like the exclusion of certain edge profiles or shorter runs due to poor mechanical strength of the stone. (Picking slabs has even become necessarfy with the latest quartz colors which attempt to provide some movement. Such slabs often have pools of resin lacking in color which many people would not want in their countertops. Inspetcing the slabs gives the buyer the opportunity to reject such slabs or demand the uncolored areas not be included in their countertops.)