No, those people (or sometimes groups of people) go to great lengths to camouflage themselves, especially after repeated bans. This is not the case of “all accounts registered to the same e-mail” or “10 different posts from the same IP address” (though those are not uncommon, too, and might be allowed if community rules aren't broken). 4chan is hardly an outlier.

Moreover, you can make hundreds of anonymous posts on your own, but if no one reacts (and considers the thing/idea/joke uninteresting), they will still remain the only replies in your precious shilling threads.