When I had a builder replace my extension he said he could also supply and fit the kitchen units using his discount. It seemed a good idea at the time, but looking back it was a bad idea. I'd employed him to build an extension, not fit a kitchen. I spend ages redoing stuff after he left that his low competence employees had screwed up.
Just my opinion but in future I'm going to employ folk to do one thing, and it should allow me freedom to get what I really want elsewhere, supplied and fitted by those I choose. Rather than get swayed by discounts or cost prices.