How much time are you going to take and how well equipped is your tool box? FYI a nice one of those will still be worth close to what you paid for it in a year.
If you cant disassemble anything or everything, I like to work the suspension a bit on both ends. observe if any leaks or oil rings appear on the fork tubes or the shock shaft. if oil appears you need some seals. suspend it off the ground. lift up on the rear wheel a little and then let it drop in your hand. if you feel clunks or clicks there is some linkage or shock bearings that need replacing. hold onto the rear wheel and stabilize the frame by pressing your shoulder into it somewhere about the place where the seat meets the frame rail. push back and forth just like the axle had arrows on each end and you are trying to follow the arrows. if you feel any of those clunks or clicks you need wheel bearings and or pivot pin bearings. I carry a torque wrench because invariably the owner will say that "they probably just need tighteing". if the axle and pivot bolt still move at 65 ft lbs they are shot. even if they do take up slack that means that they may be worn to the point of needing torquing.
take a multimeter out and test the battery before starting. should be reading about 12.5 to 12.6 volts or you write down that the battery is due for replacement. (check it again running and see if it meets specs which should be over 13 volts at least).
look at the chain and sprockets. most bikes need them because most people neglect them. the sprockets should have teeth that look symmetrical. you will probably have to wipe them off to tell. if they are not symmetrical or look like they are forming a hook, t hen it needs sprockets and unless the chain was just put on and not run it needs a chain too. look at the chain and see if the rollers have play on the pins. a pencil is kind of handy to use to pry on one roller against the one next to it to see if you get movement.
look at the engine for obvious leaks and cracks or other collision damage. this means looking underneath. carry a flashlight. it comes in handy to look down the air tract to the carburetor.
Take out the air cleaner. use a kleenex to rub against the part that is in the intake tract to the carburetor. make sure that tract is all the kleenex touches. examine the Kleenex for grit. It there is ANY at all, then the piston and bore need help. ditto the valves and guides.
Still got time? take off the left side/magneto cover and grip onto the flywheel rotor and pull up and push down hard. ANY movement at all that isnt in your joints means you need main bearings and that would be a deal breaker if I was you. So you might want to start with that one.
as you go take notes on everything you test and the results.
Then start it or have him start it and ride it away and down shift at a point you specify. see if it is blowing any kind of smoke. black is fine, we can tune that out, blue or what sometimes appears almost white means the internals of the engine are in need of help.
then ride it yourself if he will let you and see if you like it. that is really important.
I think those are great bikes and things like cables and brake pads are almost an expected replacement or 30 day upgrade so I dont waste much time there.
Those other points above like the worn wheel bearings etc can probably make you and extra 100 to 150 dollars by showing him they are worn and when he sees you taking notes he may be getting bored and worried about what else you are going to find and drop the price or offer you beer, or both.
If you find the grit I talked about, then you are going to offer something like 1k to 1150. you can get a bigbore kit while you replace things.
tires, rims for round and dings (spin them while it is up in the air and see what kind of wobbles you get).
The way I usually word things is that I give the guy a dollar figure like "i know you said 17, but if I like it I would offer up to 15. I don't want to waste your time or mine. Should I come see it?" or words to that affect. lets him know I am not going over 15 but may be offering less.
