Originally Posted by
Adam1222
Or pulled over for any reason, as you won't have any valid insurance whatsoever. (Even your credit card or personal policy won't cover you when you're using someone else's car against their explicit direction.)
Quite. It would be foolish and expensive to assume otherwise.
Your post suggests only certain makes of cars are involved, in which case it seems like a very risky thing to do with very low upside. Note that Mercedes and BMW vehicles in German rental cars aren't necessarily luxury vehicles.
All rental agencies in Germany specify which groups of cars (for example SDMR, CWMR, IWMR etc) are permitted where, and/or which groups of countries cars are allowed or not allowed in.
What is the OP's solution? Rent from Sixt, where Italy is included in Zone 1.