I bought a B.S last week. Today I did a couple of tweaks to it. Mine actually came in great shape with no real issues with it. I swapped the collar to the bearing, which did make it smoother. I also fixed the tray as far as being a little wobbly when it was spinning. This isn't rocket science and I'm sure others have done something similar, but I thought I'd share my little trick just in case it would help somebody out.
I had read about people taking the assembly out, putting it upside down on the ground and eyeballing it. That works, it was my first step, then I added a simple tool. I've spent 15+ years as a bicycle mechanic and I started to view this as truing a wheel, or a brake rotor. We usually have guides for that which aids in getting things straight. I put my basic angle finder on top of my stone in the center and started slowly rotating the tray and watching what the needle was doing. When it moved, I fixed the problem. I just put my hands on either side of my tool, and was able to force the tray. Did this until the needle showed what I wanted. When satisfied, I moved on. The needle is great because you can judge how much force to use based on the degrees off, and you can instantly see your results. Probably 10min worth of my time, and now it is pretty damn smooth. You probably couldn't get it absolutely perfect due to imperfections, but we are launching pizzas, not the space shuttle. If that helps anybody, then great.