Not sure about vendor or banking, but as long as amiable is good for a quest turn in charming should work. People do it for all sorts of quests. I’m even pretty sure that some of the turnins within the Enchanter epic requires you to charm the turn in npc first.

You can definitely bank or vendor from a charmed mob (at least on blue). Used to charm the banker in oggok and use him to kill guards, sell to the entrance guy, then bank the plat.

You can't vendor on green from charmed mob last i checked, can bank tho.