Well, on the one hand, a lot of us in the community know darn right who is an alt of whom. Secondly, most alt accounts have obvious alt names. Like let's say CX has CX, CX farmer, CX 2 and Abernathy as accounts. We all see pretty easy that he's doing shady business if he's posting on CX farmer and CX 2, and his friends know his Abernathy toons. Probably.
(Disclaimer if there's a person who took CX, I don't actually mean you, I don't know you, and I picked the letters at random)