If you want an example of a self promotion done right, I will direct you to
@nidalnijmgames and
the thread on his game.
He did not make the thread itself, but joined the farms to answer any questions and provide updates on his game. Due to the nature of his game, he would be hard pressed to do so anywhere else in this political climate without being censored or judged. As far as I know, he doesn't shill his game outside his thread and he doesn't make a nuisance of himself, in fact he's a very nice guy to talk to and he loves talking about topics other than just his game directly. When he does, he gives updates, sometimes behind the scenes sort of stuff, the kind of things you want to hear from a game dev, nothing heavy handed to force you to buy his product. I am not sure if his game is a financial success or if this thread on the farms helped him any, but I don't think it hurt anyone in the process, either. Plus, his game is pretty based, just as advertised.
If people like Nidal want to come here to promote their business or products and they're not obnoxious about it, I don't see why you shouldn't give them a chance. Some might have nowhere else to go without censorship, others might want to find self-minded people that they might find here, others want to promote something that only those who follow specific lolcows or communities like the sektur would care about. Naturally, this would be the place to do so.
This isn't an issue I feel very strongly about either way, and like I said it should be allowed strictly so we can judge each person on individual bases, depending on what they're selling or promoting and what their motives are.