The vast majority of them.
On the steel and aluminum ones they almost always get new grips. Either wood or G10/Micarta (because I like how they look and feel) generally.
Sometimes the polymer ones get stippled or have Talon 'Grips' (stickers) added to them.
Almost all of them get new sights (BHP's, CZ's, Glocks, 1911's, S&W M&P's, Walthers, H&K's, Sigs etc).
AR's, AK's, H&K 91's, PTR's, FAL's, FN Scars, CZ rifles etc are all the same way. Rarely do they come exactly like how I want them.
Same with bolt action or single shot falling block rifles. At the very least those usually get a scope (even if it comes with a scope it's always one of those package deal scopes), then rings/bases, sling, maybe a buttcuff.
So it's a rare gun that doesn't get changed in some way.