DB architecture of the user's payment account

I'm working on web api for auction web-site. The main purpose of this site is to combine sellers and customers. Customer make an order, some sellers make offers. Customer choose best offer and seller execute this order. After order has been done, customer should pay to seller. And here is the main problem.

I want to implement internal payment account for each site users. Every user can put money into account over any processing center, for example, paypal. And then this user can pay any finished orders or services. Money just simply transfer from customer account to seller account. Seller can later cash out earned money from account or pay for another services in auction.

So, the main question is: does somebody has any experience to implement payment account on practice? Maybe some code examples on github, or database schema, or any ideas and suggestions.

Thanks for any answer.