Why's it so hard to rent a villa in miami

[sinis]

We are looking to rent a villa in miami over xmas/new year. We have been looking at a site "vacation rentals".
Every time we find one we like and contact the owners to enquire about dates etc. If we go back to look at the pictures again, the villa has been withdrawn from the site. The owners send us deposit details but it doesn’t feel right. Asking for a 50% deposit based on a web page and email address. This has happened on 3 or 4 villas now.
Going through the site would give us more security, but even the site doesn’t respond to emails. Really want to book a villa but just wonder if this is all just a big scam to get deposits, for non existent villa's even though they show them on google maps, who's to say its actually theirs to rent. Have mailed and said about our concerns over scams, but just get nonsense mails back saying go look at it or get friends to check it out. Like that really is a feasible option, after all if we were trying to rent a villa we are sure we would be more accommodating in answering concerns such as these.
Anyone got any sites that they know are genuine?

[SLacKer]

Used http://www.vrbo.com/ to get a villa recently

I would only expect say 10% deposit for a villa not 50%.

[twiglove]

+ 1 for vrbo = vacation rentals by owner

[sinis]

Thanks for the villa site, will check it out.
We booked flights via last minute dot com with north west airlines for 340 pp