If your horse is 16hh, it's a good idea to get a trailer that's at least 7' tall, so he doesn't bang his head. Taller also usually goes with longer, so he will have plenty of room to stretch out and balance like he needs to. I would also ask to make sure the floors are good...sometimes they start to rot under the mats. If you go to see it, measure the inside at make sure it's tall enough, and check under the mats that the floors don't look splintered, rotting, or overly stained. Also a saddle rack in the tack room is always useful. Looks like a decent trailer though.
He knows when you're happy; He knows when you're comfortable; He knows when you're confident; And he always knows when you have carrots.