Drive it and see how it feels.
The 350 petrol M276 3.5 V6 is a peach, and pretty bullet proof too.
MPG is pretty close to the 350d and gets up to temperature within a mile, so can handle short journeys, and let's face it, the UK tend to buy petrols when they are not doing loads of miles as we chicken out in case they are miles behind the diesels.
The only issue I found with mine was it hated Sainsburys petrol 95 or 97 or Asda 95. It would throw an EML and when scanned say misfueled and NOX sensor error.
Stick in super unleaded, and ideally low or no ethanol and it will purr away for miles. I sold mine with 118,000 on it I think it was. It averaged 31mpg and would do 38mpg on a run on 98. For the first 9 months or I ran it on 95 and it was doing 27mpg and 34mpg on a run, then when I saw the German review saying it is set up for 98 I started to use it and within 2 tanks got better results, it was even smoother as well.
It is also naturally aspiration, so far less to go wrong with it than many modern cars. Still with decent fuel and the injectors etc. will also last 200k miles as well.
The W212 is pretty tough suspension wise, unlike the 211 series, the control arms etc. or rather the ball joints are so much stronger than the previous generation, and that is where a car starts to feel tired.
I have a W207 E350 cdi coupe at the moment, so not knocking the diesel, this is great, but the petrol is in a different league imho, it is a cracker, but also much rarer. Well it was in estate guise and you won't have all the EGR and DPF issues as they get older.
This e350 cdi I have at the mo had new EGR, new DPF, new dpf pressure sensor recently, which cost him a fortune, you don't tend to get all that with a NA petrol, so I wouldn't worry on mileage too much.
Drive the car, even a 10 year old one should still feel pretty much like new, if it doesn't, move onto the next one.
The problem with higher mileage cars is they tend to fall into the price where spending £1000, £2000 or whatever on new suspension seems too much, many think "I will use that to upgrade."
I think with Covid, with lockdowns and with maybe more uncertainty though we have seen people get out of the PCP game and start to buy older cars outright more, that has pushed prices up and with it made people realise that spending a grand on new suspension maybe be a better option then spending £400 a month on a new car.
Which is good, too many really good cars get a bit neglected in this country, when they get to 6 years old they are classed as old, which is silly really.