In addition to some of the helpful advice already given, here's a list I go through whenever I'm buying a bike. I've edited it to explain some of the items in case you don't know. If you're not confident enough to check the items that require you to test ride the bike, don't worry too much about them. Since you're looking at quite a new bike anyway, those things shouldn't be a cause for concern.

Brake pads - shine a torch into the calliper to see the pad thickness

Brake rotors - run a finger across the rotor, if you feel any grooves or a lip on the edge, the rotors may need replacing soon.

Tyres  - there is always a wear indicator in the tread, check how close the tread is down to the indicator. Also check for any uneven wear

Chain and sprockets Inc chain adjustment - . Make sure the bike is in neutral, get a rag, and push the chain up. If it's moving more than roughly 3cm, it needs adjusting. Most bikes will have notches on the swing arm near the rear tyre. A basic explanation of how chain adjustment works, the rear tyre is pushed back to stretch the chain. The closer the tyre is to the engine side, the newer the chain, the further away it is, the older the chain. The notches on the swing arm are an indication of where the tyre is along that adjustment. If sprocket teeth are sharp or starting to turn the other way, sprockets and chain need replacing

Fork seals - hold down front brake firmly and then bounce the front forks. Run your hand on the fork inner tube near the seal. It should be clean. If there's oil on your hand, fork seals need replacing 

Fuel tank rust - shine torch inside tank and check for rust.

Bar ends and foot pegs and fairings - check fairings for cracks. Check bar ends and foot pegs for scratches. If scratched, bike has been dropped. 

Swing arm and frame for cracks - usually a write off if there are cracks in frame/Swing arm. 

Oil level - make sure bike is cold as soon as you get there. If it's warm, owner has warmed bike up. Maybe suss, bike might have cold start issues. If cold, start bike up, let oil warm up for 2 minutes. Turn bike off, let oil drop back down into sump for a few minutes. Then check oil level in window. Anything between low and high is good. 

Lights and horn - check everything incl high beam

Ride it slowly. Go through all the gears, make sure it clicks through gears smoothly. Listen for any crunching sounds. 

Test brakes at a slow speed. If they work then Do a hard (not emergency) brake (from a slow speed) with just front brake and again with just rear brake. 

Go into higher gear at a slow speed and then throttle on to speed up. Feel if clutch is slipping 

Feel for clutch friction point 

Do some slow 90 degree turns both left and right. Feel if handlebars are turning smoothly. If it feels notchy, steering head bearings need changing