Rentals YES , Sales
you don't need to be ST certified to sell, the listing fee is $35 plus any bells and whistles and the final fee is also $35.
As to other sites, Myresortnetwork, redweeks, tug, all get some traffic. We do well with Redweeks, but we also us bidshares, and when it has to go, Ebay.
The process to get certified is simple, I think it costs $10 and $7.50 for each month of use.
You can suspend it once you've rented you weeks, and then reactivate it automatically when you list a new rental.
fwiw,

Greg