RV time shares

I was looking through Craigslist and noticed someone sell a time share membership at a RV park. I remember years ago all the invites I received after buying a RV. Haven't had a invite in years. I also remember back then visiting a parks that was selling memberships as they were informed the members at the park it was closing. No morals in these salesmen. They were pushing several memberships to a national club that allowed you to visit RV parks all over the country for a small charge. I remember people telling me stories of how they would be sold memberships to find they lost everything. Some told me their park was closed and their membership moved to a park that nobody wanted to visit. I was told by others they would call their park to see if there was any space, and was informed they were full. They would go to the park and find it only half full. The park wanted to keep the operation cost down. Are these still out there? Have they changed to the better? Do they still have the national and inter-national clubs?