I checked on Scamadvisor and they have been online for about three years, and they have no listed comments, good or bad.
All I can say is that there are so many of these sites that will list your RV on the web and that's it. They make their money $100 or so at a time, and they do put your pictures and info on their site, but they do not handle sales for you, so what you are buying is a listing on a site that may or may not get much exposure.
I would recommend that you look at RV Trader or one of the other big sites. They do the same thing but they do get a lot of exposure and have an email notification system to let you know about offers or just questions from potential customers.