Hi Ming, having had a look at the ad, I would be asking for the reg number and doing a VOSA check to ensure there are no major issues on the old MOTs and the mileage all adds up.
Will put up some pointers for you and your quest for an ML, by no means is this exhaustive, but some main things I came across when I was looking, some may be obvious and others not so, apologies if I am preaching to the converted so to speak.
Am 99% sure that DAB didn't come as standard. Apart from the privacy glass, side steps and reverse camera, it is standard. Again, saving you a possible journey, I would be checking to see if the steps, reverse camera, tints factory are from factory (if you are bothered about that). It doesn't appear to have sat nav (COMAND).
If the seats were fully electric
and memory, the controls would be on the door panel oppose to the seat base (just for future ref) like this:
Can't see a button for the heated seats (from those pics) , it should be on the centre dash. Defiantly doesn't have airmatic either, nor does it have xenon/ILS headlights which is madness for one of these but quite common, it has halogen headlights!
MLs with airmatic will have the buttons here:
Is the service history MB, Specialists or other?
The interior seats have alcantara through the middles section, this will more than likely look to have watermark type stains. This is as a result of the adhesive that MB used in a lot of their models around these years and due to some sort of reaction, owners ended up with stained seats! They did replace/repair owners affected over a period of time, mine hadn't been rectified (I bought used) so still look like they are watermarked. After much research, the only cure of this is to retrim the panels, no amount of cleaning products will remove the marks, may lessen them but not remove them. The other sections of the seats are not leather, but what MB calls 'artico' = fake leather, not the best tbh, but it is fitted to several models across the range of MBs, can be prone to cracking and I would say easier damaged then real leather (in my experience of course)
NOx sensors have recently become the hot topic for MB owners, so have a read on that (plenty of threads on here), basically IF they require doing, it can cost around the £1k mark.
The car itself (ML350 W166) has been an absolute pleasure to own, it does everything we ask of it as a family car and returns early 20's around the doors and 30's on a run, not bad for a 2T beast with the aerodynamic of a brick!
Anything else, ask away! Hope it is of some use to you.