Hi, I've just been through the same experience over the last couple of months, bought a '54 Plate DE 75K miles in late July with regular servicing for the most part reliable and am happy
Did lots of reading up on the forum and looked at about 4 examples I think the main things I specific car checks were:
Burning oil! - On cold start none of them really smoked but some had loads of soot around the exhaust for a car that had been recently cleaned and lower oil levels when serviced within 5K miles elts say. Although wasn't definite proof seemed like some were drinking more oil than others. My friend called me paranoid but definitely could smell oil in the cabin at low speeds.
Clutch health - my clutch started slipping after 100 miles got it done from the dealer thankfully as was within warranty. They all had high juddery snappy clutches around the 70K mark - OEM clutch and flywheel is around £600 fitted and supplied. one to factor in the price.
Gearbox health - they were all a bit notchy and loud when shifting but when warm flowed through the gears well and no odd grinding or servo noises! That all changed when the dealer replaed clutch and must not have used genuine Nissan trans fluid, I did the oil change myself after seems to have cured.
Other than those major things to look for some quirks I found were
The rear wiper washer motors seemed to always not work,
The boot didn't pop up because of the release springs
and the 6 disc skips! Oh and the when you try to use a tape to 3.5mm auxiliary converter thingys the tape deck doesn't like it and spits it out!
The bodies are magnets for stones and the chips!
The underbody looked rusty but on closer inspection it was mostly the steel braces or pipes the body seem to be solid
Most of the ones I saw has the bumpers off/resprayed might have been light accident damage but couldn't see any evidence although interiors plastics make it hard to see however. I don't think they can quite get the bumper on right again but no biggy
This video was good
Also found that a lot of dealers do their own MOTs where some advisories or issues from last year or few months before magically disappear with no receipts or proof of work when checking against the MOT history checker!! Otherwise some odd cabin rattles or suspension noise is common but hasn't presented any issues.
Sorry for the long post, but you now know as much as me from a month or so of ownership... good luck buddy!