good luck tomorrow, might i suggest taking a mate with you who maybe more subjective as they aren't buying it themselves. i know my cars and can spot a lemon but even i have suffered new buyers blindness so much so that a car i bought about 10 years ago didn't have the AC i though it did in the advert and i didn't check properly when browsing it. i have since learnt that lesson.
as a few tips, when pulling away in it, have both windows wound down and listen out for any clicking, its a tell tale sign of clicky axles or tired drop links. neither are car killers but they will need sorting at some point and might give you some leverage.
check the tyres, do they all have decent tread, are they all the same make and are they inflated properly. if the tyres are mismatched it would be something i would be looking at changing fairly quickly in this weather, especially if they are a crap make.
the clutch when cold maybe sticky in 1st and 2nd; this is normal. but is it still doing it once the car has been warm for 25 minutes or more.
lift the bonnet on tick over, does it sound tappety or not, whats the oil level like (check it before you drive it) has the engine already been warmed up for you; if so i'd be asking why?
look at the wear on the seat, does it look heavily warn if so i'd be questioning the mileage.
check the panel gaps round the car, and check the colour matches all the way round; will show if its had any prangs.
if you can get it up on ramps have a look underneath, does it all look the same; are are some bits alot cleaner than other bits, if so are they new, and if so why?
when test driving try some down shifts like 5th into 3rd, does it go nicely or crunch in to gear.
check the rear back box flanges if you can they are renownd for blowing and needing a new exhaust.
hope that helps
by the way i'm a nobber too as i had my wheels on my old one powder coated black as well.