well you have to assign value to your goods right? i mean you have to, they come from somwhere, either you or you bought them at some point. Or you can value them at whatever their replacement is.

You can always set them up in QB , and "sell" them to whoever "checks" them out, just put the cost as "0.00". then refund them when they return it.

Im sure there is a better way, but that was just off the top of my head