tie the amount you can borrow to quest points. currently, 40 qp --> 10k daily limit. why not have a similar structure for a credit maximum. with regards to the issue of losing items, you'd have to collateralize enough items to balance your debt. these could be restricted; you couldn't withdraw them in a pk world, or engage a monster while wearing them, etc. some items, perhaps some combat-specific items, may not be acceptable as collateral. you could also arrange the collateral in an escrow. you'd essentially be mortgaging items your currently own for something you want, and then buying them back over time.
