(I'm approaching this as an Australian, where public toilets and toilets in shopping malls / department stores are always free. But I don't mind a user-pays system.)
Another scheme is usually found at Autobahn rest stops, where you actually have to pay for toilets, but get a voucher over the full amount that you can then use in their shops.
I'd say it's a good habit to always throw 50 Ct on the table - except if the person is as agressive/unfriendly as you describe. ;)
I can't believe you would claim that point # 1 would be false.
You're talking about letting the world into your establishment to use the restroom. You should know the state most public toilets are in.
The city has now moved that into your restaurant or bar. Your employees will have to clean it, or you will have to pay for the cleaning services.
So I must say, 150euros seems extremely low for this service.
My second thought was that this could be easily exploited. I assume controllers verify that signs are not ripped down or obscured for all those receiving the grant but for 150 euro a month I see no large incentive to cheat in this program anyways.
That's exactly my point. No one uses them, everyone goes to restaurants and pubs anyway - so nothing changes.
But heroin addicts aside, you'll get drunk teenagers, tagging, careless behavior and even vandalism.
1. Participating in the program will cause you additional costs
2. Participating will decrease the voluntary payments
I have no data to back this up but my gut feeling is that neither is true. People will prefer toilets in restaurants anyway and at least the locals are used to favour them over public toilets. My thesis is that putting up the "Nette Toilette" sticker will not draw more "customers".
When it comes to the voluntary payment: It's considered tipping money for the cleaning staff, so people will probably tip the same. And even if they did not it shouldn't make a difference for you as a restaurant owner, because it's not your money anyway. At least in theory...