Welcome to the problem dealers have trying to keep their store stocked with high end gear only to be borrowed and then someone buys it off audiogon.... One of the dealers I frequent said that he has to sell 7 units of an item just to pay for his cost on the floor model. That's a lot of sales plus rent to have floor (demo) models... and you guys wonder why brick and mortor stores need the margins that high end gear offers?? Plus 2 channel gear is a dying market for retailers. Almost all of our local retailers are changing their stores to be hometheater centric because that is where families are spending their money, plus their original 2 channel customers are dying off..
The only reason the cable company makes money is not with the 5% rental but selling cables at full retail because people don't want to pay the 5% rental fee.. but it's also a way to actually save money buying and selling cables on audiogon to find out what fits in your system.
Also shipping cables is a lot cheaper than charging someone $140 for shipping roundtrip on a rental of gear... Honestly the projector rental example really does show what it takes to be profitable. Tube Gear would be impossible. Then you have to also watch out for fraud, as my dealer sold an item on ebay, the guy said it didn't work and he wanted to return it, and the buyer sent back a different serial number which was broken......
If you wanted to do a rental or tweakers (footers, isolation, and maybe power conditioning) that might be another market which would have a lower inventory cost and broader appeal.. still I think this is a great idea but there is no market for it at what people WANT to pay.