A relatively low mileage recent model won't have much wrong with its mechanicals - unless it's been in a crash, then all bets are off. But the electronics cause owners' unhappiness. And nobody can look at one car and know whether IT will or will not have problems. A fleet yes but not a single sample.
In the USA M-B dealers (only) sell recent vintage cars with a Certified Pre Owned warranty - 12 months to 100K miles. Such CPO cars are also eligible for a purchased M-B Extended Limited Warranty at additional cost - about $2,000 for one year and $2,500 for two years following the CPO.
Gamblers can buy used M-Bs quite cheap and take a chance on their repair cost, others choose to stay within the system, pay extra and know the inevitable repairs will be covered by M-B.
Repair cost apprehension isn't part of owning a luxury product, IMHO.