All it needs is the pipe wrench to turn the screw!
It’s impossible to prove he did anything wrong. I personally think if anything, he might be guilty of not replacing the calipers in the first place but did not damage them, they were already ready to fail. So now you get all new parts and I think the offer is reasonable- depending on what his idea of a break on labor and parts costs really ends up being.
As to parts, check RockAuto.com for mid-price
A call to the local NAPA or equivalent store for prices is probably an even better idea. BTW, parts stores often offer mechanics a professional discount, which won’t be on any receipt you’re likely to see.
Whoops… Did he say calipers froze, or did the slide pins freeze in their bores?
What does it matter,
Sound great to me, stuff happens! Remember one brae job, you should replace the calipers because they often fail, pass I said, I think it ws $850 at 85k miles, 160k miles brakes acting funky, bud regreases the pins and some other stuff, but certainly cheaper than 1 new caliper.