Billybob, that's a great idea!
Check this out:
Long ago, I made an agreement to iguana-sit for a couple who wanted to have a long vacation overseas.
They set up a credit card account that my exotics vet could draw from, and I got a moderate down payment.
They stayed in touch for about two months, making small payments to me, and then dropped off the map. They had swindled me, using me as a dump for their iguana, figuring that I was advanced and was well known to the GIS community, so I would take good care of their ig even when I realized I was stuck with it. I can't remember, but I no doubt re-homed it, not that it was an easy thing to do.
So there is some risk with iguana sitting, and probably pet sitting in general.
Even so, your idea sounds good to me. I will check it out.