Personally I don't expect anything when giving stuff for free, just that the recipient does the same for someone else when s/he has something no longer wanted/needed.

I think your approach is lovely. The giver-of-free-stuff is not expecting anything, and a small (few francs) thank-you gift is a pleasant surprise, without creating any awkwardness on either side.

So far, I've not been on the receiving end of free-stuff, but I'll be adopting your approach when I am