I found it interesting to learn that you are supposed to give a small gift if you accept something being given away free in France or Switzerland.
We don't do this (expect this) in Denmark, nor did we do it when I was a child in Scotland. I don't know whether it is expected in Germany - I hope not, as I have sometimes taken something that was put outside a gate with a notice stating that it was free if you wanted it, and it never struck me that the person offering it might expect something in return.
I would, and most Danes would, give a small present, usually a bunch of flowers or a couple of bottles of beer, or a box of chocolates when thanking someone who had done me a favour, unless I had already offered some form of recompense, such as paying the petrol if I had been driven anywhere.
Anyone know what you are supposed to do in Germany?