The torsion bars are guranteed for life. I think the problems are rare, but some folks have had to get them adjusted. I would suggest you become as familiar as possible with how a properly adjusted TM opens, then open & close the prospective unit a couple of times to see if it behaves normally.
Basically, the torsion bars open the TM a couple of inches as soon as the latches are released, so when closing, you have to push against that spring action to close them. A "bounce" can help here. Press down with your foot in the stirrup, let it recover up, then press down hard to get it to lock. That also gives you an idea if anything is in the way inside before any possible damage.
That reminds me of another good idea: stick your head in each end of the TM before letting a shell down. You might find something like "Whoops, I forgot to take down the hanging cabinet". Don't ask why I suggest that.
Another issue is to not open it on a slope. The TM should be level to open or close it. The torsion bars are adjusted for level conditions. If not level, you can have side-to-side friction or if front to back, one will open real easily and the other takes a lot of grunt.