I don’t see any problem with people adding their own businesses to OSM. So long as it actually exists on the ground, is tagged correctly, and not copied from other maps.
I wouldn’t consider this to be spam.
I haven’t yet seen any spam around here. Sometimes, borderline cases are discussed on the mailing lists or forums, where people add their own shops or restaurants and tag them in a somewhat unusual or incorrect way (even though the core information and placement is correct). That’s usually resolved by changing the tagging to something matching the accepted standard, or inventing a new tag where none exists.
The situation might be different in larger German cities, though. If some edit was clearly spam (that is, it’s obviously incorrect and cannot be explained with an user’s lack of experience), I’d just delete it or ask for a revert of the changeset(s).