I was reading another post about giving a customer a credit and coupons were brought up, with some of the shortcomings, and workarounds were suggested.

What if we could offer gift cards?

Something that is either a gift card code (like Amazon uses) or an actual card.  If it can be an actual card, maybe we could have the option to have our own images / branding on them.

The coupon workaround has flaws.  Either use the entire value of the coupon for one order or loose the balance.  Giving multiple coupons adding up to the total value forces clients to place several orders since you can't use more than one coupon at a time.