" Still trying to figure out posting pictures. "
I had the same issue trying to get images in the forum posting and came to the conclusion that the files were all too big.
In the end I set up a free Flickr account and that seemed to work fine with the gallery URL in the forum posting reply as a link like this:
<
https://www.flickr.com/photos/194076837@N03/albums >
Good luck with the sale !