He's not complying it's time to get the police involved.
Spot onpolice will laugh at you and tell you to go to civil small claims court in all honesty.
It's not the basketball card aspect it's the way he paid and the amount it's a civil matter, the police won't waste time on small fraud claims.The police are likely to laugh this one off... so you transferred some money (lots Im guessing) to a guy you dont know, over the internet, for some pretty cardboard? I mean, we all get it, because we are collectors... but good luck trying to get the police to take this seriously man.
I really hope you havent been jipped dude. Thats just wrong! best of luck mate