Well, I don't know where you live, but where I live, if you're entering the roundabout, and cause an accident by not yielding to the person who's already inside

Well, I don't know where you live, but where I live, if you're entering the roundabout, and cause an accident by not yielding to the person who's already inside the roundabout, it's entirely your fault and you (or your insurance) pay the damages. So anyone who's inside the roundabout can be pretty sure that nobody will slide in in front of them.