Welcome Dani77.

I've a couple of favorite dealers in Beijing, but they treat me well (usually) because I have bought a few new bikes from each. YMMV (Your Mileage May Vary). For example, I recommended one of these dealers to someone, and that person had an unpleasant experience.

What I'd suggest is checking out the EICMA motorcycle show that will be in Beijing in early July. You'll get a chance to see lots of different models, and be able to ask the reps which dealers in Beijing carry each brand.

Good idea re 250cc - more than adequate for Beijing, in and out of the city.

Happy riding!