maybe a little off topic, two points on above discussion
as far as being repayed by scammers or risky/wild transactions, some (only some) cases fall into the klal of heniach maosav al keren hatzvi, most cases dont but being that you are the motzi it can be difficult to get your money back in bais din (its another reason not to lend s/o money you cant evan win in b'd)
borrowing from a credit card many would say he never actually borrowed from you but directly from the bank (this does have ribis ramifications ) and therefore he owes them money and not you , the fact that you are left with the bill, bad credit, interest, ect would be grama or garmi. just another reason why you may never see your money back