Usually I don't run into these issues, but when I do it's very frustrating. In my recent games I've had a troll or two just ruin it completely. Last game a player roamed from lane to lane soaking up xp and then feeding. In addition to that he would spam fall back pings and report "x" player in all chat. Conveniently, he had a buddy with him and they would insta hit no on the surrender vote. As the game ended and he was requested to be reported his comment was "sure ban my smurf account" which lead me to ask the question, is there any possible way to IP ban a person? If his account is banned, will he just be able to make 5 more accounts and troll games when he is bored?
I'm sorry you had a bad experience like that. The short story is that players can spoof IP addresses and get around such a system. The other short story is that anyone playing from a PC cafe would be able to get that entire cafe IP banned, making other non toxic players unable to play.