Accidentally shift to N, maybe.

But now days transmission will most likely block you from shifting into R without stopping completely.

while driving ?? did anything happen??

now that the w205 is ckd, will it be garbage as the 3series?

whats your definition of 'garbage' for a car thats over 200k?

but if i ask every dealers, they will sure say everything is all good 100%
which is why its unlikely to get an honest comment if i ask them..
i asked bmw salesmen,they bash about mercs,when i ask mercs,they bashed about bmw

Haha seriously you need a test drive to get the feeling of both cars, all cars eventually for issue but you get warranty.

Service wise W205 is expensive if you dont bugged your SA for service vouchers.
F30 get 5 years included which is good.

Interior wise W205 is much better, handling wise F30 is much better. It really depends what you focus and need really.