Heh, one of my friends wrote a negative review about his landlord's Immobilien company. Got sued and had to pay him the amount of his deposit.
I bet I'd be at risk of getting sued in Germany even if I wrote a positive review about a company. The moment you post an opinion online you are opening yourself as a target.
Germany is not customer-review friendly. I got two legal threats over a non-descript 3-star google maps review of a deeply mediocre Restaurant for maliciously damaging their business reputation. Google made me provide receipts to prove I had been there.
I bet I'd be at risk of getting sued in Germany even if I wrote a positive review about a company. The moment you post an opinion online you are opening yourself as a target.