Well, I registered at the site, and....
Enter Trade
Coineta needs passwords from both senders to guarantee that money were send from both of them. Passwords are never stored and only cached in memory for the duration of the trade.
Oh well, tell me, do you have a fresh, brand new IP address, not used on any other Paypal account, for each Paypal account users use on your site?
You know what Paypal will do when they notice the same IP address logging into lots of different accounts? They will close the accounts, request ID + utility bill for each of them and freeze the funds for 180 days.
That's what will happen.
Unless you are really clever and assign an IP address to each account, and log-in only from that unique IP address, also a unique web browser User-Agent string, and other stuff that browsers present.