I do alot of buying in China. for me the easiest tell no is watching the sweep of the movement, and on the rollies the pearl is a give away of a shitty one.
If you have a look at a low beat movement and then a high beat movement, its actually rather easy to spot in a 2 second look. I find the best way to see the higher quality stuff is to start by asking for a "automatic with chrono" this way they know your willing to spend some cash. Then can ask to see similar higher quality stuff.
With the chrono's watch for the movement sweep, as you mentioned you dont really want a low beat 7750, although ive had good luck with mine so far!
Good luck