There's quite a lot to check IMHO and best to get any works done by the dealer before final payment.
Off the top of my head :-
1, Check for service history if 1 year old (or older) and make sure this is done.
2. Check all software / module updates have been done and get the seller to put in writing what exactly the version number is for each update.
3. The later software seems much better than older software for Lane Keep Assist - LKA, drop down shortcuts, ACC cruise control adjustments, bluetooth connection not dropping etc etc.....)
4. Go for a long test drive and listen for any vibrations / rattles etc. and make sure you are happy with everything. Go on the motorway and check for any excessive wind noise and any other noises.
5. Check all four tyres are a matching brand and check for even tread all round.
6. Check underneath for any bulging undertrays.
7. Check under bonnet for insulation pad on bonnet underside.
8. As above check the car is not tied/registered to any previous owner and get the seller to pair your MG phone app to the car before final payment.
9. If you are going for the SE SR model - during the test drive when on the motorway, floor the throttle for as long as you can and check the power level is maintained.
10. Check charging cables are present (at least a Granny Cable should be present) and check the car charges OK both on AC and DC and check the charging lights are working.
As EV's are poor sellers at the moment take your time looking at potential cars thoroughly and get as long a test drive as you can to try out the car on all roads and surfaces. Before buying one go over it with a fine toothcombe for any bodywork issues (a friend or two would help !!) plus that everything works OK inside including Apple CarPlay / Android, all doors, locks and windows working, all lights working, functions, screens and menus etc, temperature displays, no bad scratches on dashboard etc.
Finally as the buyer remember you are in the drivers seat !! (especially with low / poor EV sales at the moment). Insist on getting things how you want them (software updates, etc) or just walk away to another better dealer. Once you have paid, their attitude (MG) may change dramatically (as it did for me).