They are indeed solid little beasts
Most people don't believe me when I say my car is 18 yrs old. It sounds like a long time and i guess it is, but in general you can be assured (most) people who own these kinds of cars do take good care of them. You can see if they have been 'let go' as it were, and who keeps things tidy.
Any kind of service history they can provide you with is always good. Some cars come with a hand-full of receipts/invoices in the glove-box. If you see things replaced that indicates something dodgy went on, like a smash repairers receipt, beware
Ive had mine for just over a year now, and he's not skipped a beat engine wise, only comment that i noticed people have with GTS-Ts relates to idle issues, but they are easy to troubleshoot and usually easy to resolve
I did have a minor bingle but that was mostly cosmetic, and my own fault...