I used to take collateral, which was access to an account with at least the value of the loan on it. I got it in writing from the loanee that if they didn't pay me back, I was authorized to take the money off the account. Via selling ships if necessary.
It only became necessary once, and I took the remaining loan principal, plus the interest I was owed, and deleted my access to the account.
But when /movechar became an option, I closed down my loan service. I'm kinda working on a way of getting back into it, but we shall see.
Also, bounties are completely ineffectual and kinda pointless as they don't cost the bountee anything even if they get blown up.