I have bought a few BMWs out-of-state. All but one were new. What I learned is to tell the out-of-state dealer that I will register the car myself in my state and he will not bother. That is the simplest way as there have been times when dealers offered to register and things got screwed-up and I ended up registering myself.
You bring the car with temp plate to your state and then take it to DMV to register. No middlemen costs.
Good luck.