my rear wheel wobbles while it spins, like in this video. I read in the comments that it could simply be a badly mounted tire. What's your advice on this, what should I do?
The video indicates the wheel is out of true. It can be a real hassle trying to true the wheel yourself if you don't have proper equipment and the experience to perform the job. I suggest a trip to the local bike shop and allow an expert to save you some frustration. It shouldn't be that expensive because your wheel isn't all that bad. At least it turns and that's better than some wheels I've seen!