There is no reason to be nervous about Redweek and you can use paypal to pay, regardless of where the rental is advertised, if the other party agrees to it. Remember that the other party also has to join Redweek which means that they are probably not there as scammers, because they have to provide Redweek a valid credit card and contact ID to join.
What is it about Redweek that you are concerned about?
My suggestion - offer to pay a $100 deposit up front and the balance when you receive the confirmation in your name from the resort or from Redweek.
Redweek also has an escrow program (for a fee) if that makes you feel safer.
However, renting only one week ahead can be problematic in getting payment and paperwork turned around in a timely manner.