Usually, a vendor does not get paid to sell his goods.

Yet, that is exactly what peer-to-peer lender Prosper is doing, and in the course of one week has been forced to raise its fee to its vendors.

Prosper’s “vendors” are, of course, its lenders who are “selling” their money to borrowers. (I know, borrowers rarely, if ever, understand that they are actually “buying” a lender’s money, but that is exactly what they are doing.) Last week, Prosper began offering its lenders 1% “cash back” on the money they lend. And then last Tuesday, Prosper bumped up that payment to lenders to 2% of loans made, as long as the lender extends at least $25,000.

I wonder whether these offers are a sign of desperation at the pioneering P2P lender. One of the sad truths of P2P lending is that it requires … lenders. I tried to determine whether lenders are in short supply at Prosper, and was unsuccessful, although I would suggest that these offers imply that they are.

And I’m not surprised. Prosper has never recovered from its 2009 hiatus to complete its registration with the Securities and Exchange Commission. From March 2007 to March 2008, Prosper originated 11,453 loans with a face value of $81.8 million. But from March 2009 to March 2010 originations fell to 2,808 loans, or $12.6 million. In the year ending today, Prosper has made 5,975 loans, or $30.5 million — better, but no where near Prosper’s peak.

This doesn’t surprise me. Prosper freely discloses that its net charge off rate is 19.6% — and that brings me to an important point that was lost during the P2P craze a few years ago: that lending is hard. I opened a Prosper account back in 2007, but I’ve never made a loan. Each time I’ve thought about it, I came back to the same realization: I am not an underwriter. Underwriters get paid to underwrite loans; what do I know about making a loan? Nothing.

Now there is a little 2% bribe in it for lenders, but I doubt they’ll bite. With the economy improving, there are far more worthy investment choices than there were in 2007-2008, when the recession took hold. And that spells trouble for Prosper, and I would think other P2P lenders out there.