What to ask when considering an older T@B?

Hello,  My husband and I have been looking at T@Bs since last fall, and have started considering an older model instead of a brand new one.  For those of you that have older T@Bs (2010 and earlier), what questions should we ask when inquiring from a private seller? I am very familiar with the 2015 T@B S as that is the one we were looking at last fall.  However, we are completely out of our element with the older T@Bs.   One thing I think I'm correct about is that the older T@BS come with surge brakes instead of electric brakes.  

We want to be prepared with the right questions should a good listing come up! Thank you in advance for your help! We really hope to be T@B owners eventually! 

Krista