How do this work?
Someone send 0.1BTC and then someone else send 0.1BTC too and first one get 0.12BTC isn't this site now 0.02 at a loss? And every time someone send site lose minimum 20%
Person 2 pays for person 1, person 3 pays for person 2, etc. The last person is screwed and the site doesn't pay anything (most likely some sort of fee for doing this).
If site have received 100
BTC they have payed 120
BTC so last one need pay more than 20
BTCSo if everyone send under 20% of total received amount they must screw many people or they lose.
EDIT: I got it now if second doesn't cover first, third pay first too.