What is the best way to buy yoyos off of other players? Do I just ask? I’m curious because I’ve saved 250$ for buying stuff at cal states and I want to get a good deal on a few throws.
I don’t think you have to worry about that. Most people ask you if you want their yoyo. 
Just ask politely. Alternatively, vendors usually have good deals at contests too.
Also, buy B-Grades (That is, if it is a yoyo you plan on keeping for the sake of the yoyo just playing really good. If you’re buying it just to trade it then get A grades haha)
Just ask “Im looking to buy/trade got any yoyo’s your willing to part with?”
Or ask “got any yoyos’s for sale?”