MrKnowItAll is a SCAMMER
300% interest on a one week loan? Hopefully you only have to get burned once to learn that's too good to be true.
Smaller loans require higher rates of return to make them worth doing. Would you loan someone a quarter with 10% interest?
To be honest I didn't think someone would bother to scam for such a small amount. It hardly seems worth the effort.
I look at loans the other way around. Loaning someone a quarter exposes me to much less loss than loaning $100. Also a person who is in need of money is much more likely to be able to get their hands on a quarter than $100. Realistically we don't have enough info to determine a valid interest rate, but I would definitely be charging someone more if they wanted $100 from me than a quarter, but to your point I probably wouldn't bother loaning a quarter to begin with. Sorry it didn't work out for you.
Loaning a quarter has less risk, but at a low interest rate the payback is not worth the overhead of servicing the loan. That's why a mortgage lender will loan you $500,000 but not $500.
The MrKnowITall loan hit me at the risk-reward sweet spot. The loan amount was low enough that I didn't worry about losing a substantial amount of money (around $10 at the time), but the reward and short payout time was enough to be worth the risk. It also seemed unlikely that a user would hang around long enough to get out of newbie jail, including making some substantial posts, then throw it all away for $10.
My theory is that the borrower did not originally intend to be a scammer, he's just a bad gambler who hoped my loan would turn his luck around.