First off, Ping Rocks! QA is there, Customer Service is there..
Second.. That $600 does not include shipping.

Third...
RUN, FAR, FAR AWAY FROM ANYTHING ON ALIBABA..
1.) It's barely a 50/50 chance, you MIGHT get a real company..
2.) THEN a 50/50 chance that you actually GET the product.
3.) THEN a 50/50 chance the product actually is what's advertised...
That's about a 12.5% chance of getting a decent product..
4.) If not, then you're out your money with NO RECOURSE!
(Alibaba is riddled with fake companies, bad items and alibaba always sides with the seller)

PLUS.. although the first link only showed $250-$300 that does NOT include shipping which will be at least $150 and then you still have to worry about items 1-4 above.

If $600 is out of your price range, get a smaller batter and pedal.. LOL..

If you give us an idea as to what you need it for, we might be able to help you better..
What speed do you need?
What kind of motor?
What amperage is the controller rated for?
Etc.

If you really NEED a 48v 20Ah, expect to pay a minimum of $530..

Questions, comments, queries?..