"Before You Buy" checklist

As we search for a gently used TM (no more than 10 yrs old), what would you suggest we be sure to lookout for? Leaning to a 2720SL if that makes a difference.
Other than checking in the wheel wells for damage during a blow out, and testing furnace, AC, etc do you have advice?

Love this site. The checklists by Ed Felker and the Manuel by Mike and Kelly are very helpful. Looking foward to having a TM!