Is $12,000 to install quartz countertops and backsplash a fair price?

My kitchen countertop and backsplash are about 120 sq ft. I got a few quotes and they are so much different with the same slab. I'm not trying to go for high grade quartz; the one I'm getting is Calacatta Vatican. I'm questioning if the $6.3k quote is too good to be true, especially since they were recommended by a marble company. I did confirm with the second guy that it's for the quartz.