I tear apart medical and other machines to recycle parts. I do often see 3d printed parts inside commercial machines, probably because they are making so few of them and it's more economical to just print a couple specialized parts.
I don't have a 3d printer myself so maybe it'd be obvious if I printed some.
I say most because there are finishing methods which can largely obscure these details and make it less obvious as to which method produced a given part.