We've rented homes a few times and always had to pay up front too. We were always able to use a credit card and as long as our stay was within 60 days, I felt like we had some protection.
I don't know if I could pay cash up front to be honest. Do they have any recent renters you could talk to?
It's been a while since we rented (we bought a TS in Kissimmee in '05.) but last summer we drove through the ol neighborhood (Rolling Hills, very close to Indian Creek) there were a lot of forclosure signs and sale signs. Also back in 05, there were very few permanent residents. Now there were lots of mailboxes along the curbs, something we rarely saw before.
Sorry, I'm not much help but I'm not very trusting. I'd rather pay more and go through a company that would stand behind me. Back then we used Villa Direct but I've heard so many bad things about them here on the Dis I wouldn't recommend them now either.
Good luck and hope you find some info about your seller to reassure you.