Welcome rneibeck. You will find the people here very friendly and helpful. Check out the Sunline Community forum and thread titled "Sad Video, Early Death of a Sunline"
Needless to say you can't do exactly what this "dealer" did to a private purchase you are interested in (although if you do....by all means get it on several cameras from different angles with close ups of the facial expressions....it will be a hit for sure).
This trailer had some very serious damage and this guy knew that going in. His scare is to have the dealer sell you. That said, it does have some very good points to look for and they are presented in this video as a visual aid. He also was surprised when he went into the corners expecting damage only to find they were in pretty good shape. Read his voice tone and you can get a "feel" for his "tell".
I'm new to the Forum myself and trying to and have learned a lot. I have a 1983 T-1550. It isn't perfect, but I love it. It is my 1st trailer but very well may not be my last Sunline. They're collectables aren't they?
Again, welcome and enjoy.