Well played Paza!!
First service interval 1200 miles which is the most important walk away otherwise.
Obvious car checks, suspension probs one, check the strut braces these can crack near the strut tops, creaking at the back can mean worn anti roll bar bushes but theres nothing really that is renowned for going wrong. Their pretty bullet proof, service intervals are very important as long as the history is good I would say go for it. Get one with the best pos spec obviously lol!
Have a quick shifty at brake pads you can see the depth if you turn the wheel to its furthest point and get down close, and obviously the discs these can have lips and a full replacement is expensive. Obviously tyres make sure they have good tread because again another extra you don't want to pay for, and they are suitable for the vehicle. Just obvious stuff.
Servicing if it is low milage see when the next service is, low milage and long periods between services can be worse than higher milage cars that have have had more attention. Especially if there isn't much warranty because if it needs some parts. Also Check when the Inspection 1 or 2 is due depending on milage. Mine had 46k when I bought it and was due at around 52k I think but because it is lower than average milage and costs £800+ and the service interval was quite large I got them to do the service simply because I didn't want to pay for it a few months down the line and they could fix unnoticed problems before pick up.
Check the alloys for erosion mine had a lot of pitting so had them refurb them before pick up too.
My only advice is get one with a warranty because these cars aren't getting any younger and other things crop up, usually not mechanically.
Mine has already had around £1500 worth of warranty work done only had it 6 months. It may take a while to iron out the creases. New ECU, new drivers window motor, new front left calliper, also had lots of reprogramming etc because of elec problems, keys have been pretty poor too all done under warranty but is perfect now no problems at all touch wood. Mine is a 56 plate and has just turned over 50K but I managed to wangle a 2 year warranty which is why I bought it, otherwise I probably wouldn't and would have kept looking. Feels like new to drive tho so I'm very happy
Simple stuff really! Hope this helps and hope the car is a belter. Only problem is you will end up buying one in the next few months if you test drive one. When I test drove the Z4Mc the 3.0SI just wouldn't do. The noise, drama, power, engine and all the typical M stuff is an awesome experience!
Life is too short enjoy mate!!