[PLEASE HELP ME] ECommerce help!

Hello I am trying to sell digital goods. But i’m not sure which plugin to use where are just too many to fully understand which one is the better one for my needs. Basically I sell accounts. And Everytime somebody will purchase using paypal or bitcoins They will get there account for that specific product, but i do not want it to be sold more then 1 time per person. basically I don’t want to sell a product that has already been sold to somebody else.

Any idea?