Carwashes.  Just ask and they will clean it for you.  I pay about 10 rmb in Shanghai.  They do a really nice job as well. They can make scratches less visible and what not, all included in the price.   I would imagine most if not all carwashes will do it.  You might be the first person to ask, but I bet they won't turn you down. At least none of the ones I've been to have turned me down. 

I bought a bucket and a brush and some towels and washed my own scooter. I wanted a candy apple red scooter, I never got past the first white one we saw, GF liked it. I hate white on cars ,anything, and its hard to keep clean. It gets almost as muddy on city streets as something I went 4 wheeling in at home. I can wash it in less time than I could take it some where and then wait.