Hey Lee,
If this last 80/90 sold on the bay is any indication of a trend, this might not be a bad time to unload your 90. Videos are good, but make sure your chain is razor sharp and it looks like you're cutting FAST. The 'chainsaw guy' outa Oregon who made hundreds of youtube videos selling saws, always made sure he cut into softwood. His sales method was usually to show a saw running on the bench, goose it a bit, talk about the saw...then in another video, he'd take it outside and cut some doughnuts in softwood. You don't have to get that involved, in fact, you could just start and run a power head to good advantage. I wouldn't volunteer any faults with the saw in the auction. However when they ask you questions in PM, just be honest.
In lieu of using a video camera, show LOTS of pics...buyers like a plethora of pics(don't forget the bottom). Buyers aren't supposed to assume that you don't have a good camera or lack the expertise to post numerous pics...we take just a few pics offered as the possibility of trying to hide something about the saw. Best of luck if you do decide to sell!!
Kevin