These groups are local (Weslaco area) Facebook Groups or RGV Valley groups. The are public groups, can be searched and found on Facebook, and for everyone to join. In some cases, you can just join, sometimes you have to ask for permission, and when that administrator grants it yow ill receive a Facebook notification that you can now enter the Group.
Until you join, or are granted permission to join a Facebook group, the direct link won't work. Once in, you can enter it directly.
This is a great way to advertise your trailer for sale or rent, for free!!! Just post pictures, or video.
Anything you put into these groups can be seen by anybody. . These groups are very active and your posting will reach thousands of members. A quick, cheap way to advertise.
Have fun with it.
A simple sample of how to request to join is shown below. Click to ask to join the group. Once joined by the administrator you will receive a Facebook notification. Look below to see how to confirm membership.
Click below to access the direct link to groups after you have joined