I recently had people in to quote for various things.
One job the driveway I was quoted £2k £1.6k and £1k
The guy that wanted £2k phoned me chasing the quote and said he could do it the in a couple of days due to a cancellation
I told him I'd been quoted £1k and he said he could do it for £1k
"So u were planning to rip me off essentially"
The guy who got the job was the £1600 he suggested a couple of things that were good ideas that showed he knew his job.
He also got the job to do the groundwork for the extension, without getting other quotes because he showed me he knew what he was doing, wanted to make a descent wage for doing a descent job but didn't want to rip me off.
Cheap isn't best.
The guy who knows what he's doing is the best guy for the job.
In the OPs case he initially said that he was happy with the guys work and the price(I think) just didn't like how he had priced the quote.
A phone call to ask may have got you what you wanted by the original installer.
He felt u would rather not pay "high" "labour" charges. So he did his quote in a way that reflected that.
You say you've now saved £2k I'd be worried about someone doing a job £2k cheaper for the same job