Maybe there are regional effects at play, but in almost every country I’ve lived or worked in there are a substantial number of independent iPhone repair stores, usually with cliched names like iRepair or similar, and many of them seem to be doing a roaring trade. If people weren’t using them I can’t imagine these stores would be continuing to exist in such numbers either.

Outside many European Apple stores they even often pay someone to stand and hold a sign advertising cheaper iPhone repairs available around the corner etc.

Anecdotally, a large number of my friends and family have all used these, usually for cracked screens or batteries, and often in preference to an Apple store on the (sometimes incorrect) assumption it will be cheaper than “taking it to Apple” to get fixed.