I see people making 2 accounts on forum. It's completely fine as long as you don't use 1 to give good reputation for the other in every post. it's like licking your own balls and it's pathetic.
Sometimes, I see a stupid post, where the information is just wrong and retarded, and someone else actually liked it. So I check out who would like such a thing. Turn out, that account has been created for almost a year, but its activities are nothing (only 2-3 comments, no sell, no buy) but giving likes to the owner of the stupid post. This is a strong evidence that the two accounts have the same owner.
Maybe I'm wrong but if you are doing this, stop.