Assuming you already familiar with the basic of analog scope, if you know the exact model, suggesting :
- If available at the net, download the user manual and spend some time to get the feel and with adequate know how on how to use the knobs and switches for that particular model. This is important.
- Certain high end analog scope has diagnostic routine can be triggered manually by pushing certain buttons or knobs sequence, memorize it if that model has it.
- Since the seller has the FG, this is very good and just make sure they have the coax cable with bnc and bring yours if they dont, I know this sounds trivial, but it will very annoying if you stand in front of a scope and FG but dont have the accesories needed, also small thing like terminator, scope probe if you have one and etc.
- I assumed you have some sort of diy voltage reference, no need for ultra accurate, bring it too, once verified against your dmm, this at least it will help you on checking the vertical accuracy.
- Make sure you can have enough time like turning the scope on say for 15 mins to see if its stable enough.
Had similar situation when I bought my tek 2465b, and if somehow you spotted any inaccuracy say like vertical against your vref, this might be reason to bargain for a better price.