"Able to" implies a physical possibility to me, as in the corresponding noun "ability". I can (am able) to walk, he can (is able to) speak English. For example, I personally wouldn't understand "he is able to speak" as meaning "he is allowed to speak". "Can" can imply both "is able to" and "is allowed to", but they are of course quite different. Further, associating "able to" with a person is natural, but with a shop it's weird.
I have never heard of the adjective "inable". I know the noun "inability", especially frequent in the combination "physical inability"" and I know "unable", which to me is general - someone is unable to do something because he or she is either not allowed to, or physically cannot.
Doesn't that get confusing? Because "sprzedawać" is in the infinitive, it seems to me that "może" is talking about the store's ability to sell. If "sprzedawać" were conjugated, it would seem to me that "może" would rather refer to the rest of the clause, in that it's a possibility that a store sells wine. Does that distinction make sense? And, given that, wouldn't "Ten sklep może sprzedawać wino" be a bit different from the other context?
I'm not exactly sure if that's what you meant, but doesn't the comment from immery below answer your question? https://forum.duolingo.com/comment/14219851?comment_id=19489233
there is a subtle difference- "móc-może" as modal verb is followed by infinitive "sprzedawać"
if "może" were "perhaps", the only verb "sprzedawać" would be conjugated. "Może ten sklep sprzedaje wino".
Also word order in "ten sklep może sprzedaje" sounds unnatural, while "może sprzedawać" shouldn't be separated.