Wyndham allows renting, provided you get a Guest Certificate.
Just because someone has a timeshare listing on AirBnB however, does not mean that they have every day available. I have not listed a timeshare on AirBnB but I have listed specific one on homeaway/VRBO. I list certain days that I have available and block all other days. But if you do not put the entry in correctly the calendar loads as all days available. Perhaps some listings are left with an open calendar.
So even though it is listed in AirBnB it might not really be available for booking, but it looks like it is. I know on VRBO I get requests for dates that I have not even shown I have available.
Now on the other hand if you see availability in Wyndham's Extra Holiday website and it shows available it really is. Wyndham's extra holiday site is a combination inventory they might still own, they are allowed to take at the 60 day mark, and of individuals renting out time they have booked.
(Note: owners renting option is a bad deal IMHO, as you might give them a week and they rent a single night of that week and then take 40% commission on that one night, while you are still out the weeks worth of MFs, plus you have to take their word they rented it out. Not for me to do it that way, but others have.)