This sheet is super helpful, thanks for sharing!The twill option is the best quality option. You'll know it is twill if it looks more like fabric than plastic. I would be hesitant to by the black diamond used, if over a few years old.
Look for signs of wear in the folding sections. I'd be wary of any discoloration in those spots.
Definitely make sure you have all the hardware. Check out the photo and instructions attached.
On a side note, the top can get squeaky. I've been worried that torqueing bolts behind the driver and passenger too much could break the clamp. I just get them good and snug, and I used squeak tape on any top-on-plastic ad connections. Keeps it quiet.