While there is no way to completely prevent someone who is determined to engage in fraud, there are ways to gain a level of comfort that is right for you. In my experience, rental fraud is very limited.
As Denmage said, a call with the
DVC owner is always a great thing. You should also check the Orange County property records to verify the DVC owner actually owns the property. That can be done all online. Go to:
http://www.occompt.com/ and click on "Records Search" on the right.
Looking at the owners "post history" on the site you're using will also shed light on their character, legitimacy, and experience renting. Ask for references of people they have rented to in the past.
The owner should be willing to make the reservation before you provide any form of payment and provide you with a confirmation number and screen shot showing your particulars.
You'd also be surprised what a generic internet search will reveal! I once found a owner asking way too much per point for an existing reservation and decided to do a little research based on some of his comments. I was able to determine that he recently went through a "quetionable" bankruptcy and a had a few other concerns in his past that I was not comfortable with. It might of worked out fine renting from him, but I would not have been able to reach the level of comfort I needed to do business with him.
You can do some or all of these things in order to gain the level of comfort your're happy with. Any one of these checks does not guarantee legitimacy, but in most case if you take the totality of the circumstances, you should be able to easily find the right transaction for you. I've done it many times with NO problems

. Good luck!