Gunsmiths are interesting creatures that follow the same “least effort for acceptable results” philosophy of machinists, but have some unique ideas from time to time.
Some will simply say no, they headspace all their barrels to some tolerance above minimum and you get what you get. Some will say sure, and use a loosely goosey reamer that’s on the large side at no charge, but your brass will fit. Others will say sure and spend the extra time and charge the shop rate for whatever it takes - shop rate gets expensive if your existing chamber is fatter than his reamer and he has to source another reamer just to get it to chamber, let alone the time to headspace on the case.
Being the old curmudgeon that thinks in terms of what can go wrong, I’d worry the guy can’t get your case to fit in the new chamber and instead of tracking down another reamer that may or may not work, he just opens up the chamber with sandpaper on a stick, or takes a worn out reamer and grinds off the shoulder and neck so he can run it further making the body fatter, and leaving behind some weird ring or groove at the shoulder/body junction. Gunsmiths have done some real whoppers.
Odds are the guy has good judgement and it all works out fine, but anything out of the ordinary drives up the odds of unintended consequences.
