I've noticed a lot of the loans on this forum are run a bit like:
Borrower: "I need X coins at Y interest rate, please send to address A"
Lender 1: "I sent X/p coins to you. Please return coins to address B"
Lender 2: "I sent X/q coins to you. Please return coins to address C"
The issue with this is that there's nothing connecting a forum post to the transaction they claimed to have made. Of course, chances are the real lender will post immediately and first, following a transaction, but a sneaky scammer could easily actively listen on the bitcoin network for transactions to address A and claim to have made them on the forum. Then we'd end up with two different people claiming to have lent the same amount of money to the same person, and we'd need a way to resolve the conflict. In most cases, there's a residual amount of coins that gets sent back to a new address in the sender's wallet, so it's sufficient for them to show that they can spend the residual amount, but it's a hassle.
As a safer system (at least until the bitcoin system supports arbitrary proofs of coin/transaction ownership), it'd be fairly simple for a lender to express a desire to lend X coins on a thread, then for the borrower to privately send them the amount followed by a small random sequence of decimals afterwards (X.01321451). Then, when the borrower receives an amount for that denomination, they can be sure that either the lender or a corrupt forum admin sent them those coins, and both parties can publicly post the agreement on the thread for witnessing by other people.
It's a bit more complicated, and might not be worth the hassle for most people, but I figured I'd suggest it or at least point out the flaws with the current system. Reputation can obviously help resolve disputes, but even people with good reputations can have their accounts compromised and wreak havoc on everyone