I actually made money accidentally with a BahnCard subscription.
I canceled my BahnCard 50 within the first 14 days (which they have to conform to due to laws) via email (btw: before the starting date so I did not use it). They confirmed and send me back 100Euros too much money. Why 100Euro? I had originally used a coupon code that saved me 100Euro. Good guy as I am I told them via mail that they sent me too much money back. What did they say? No, can't be, Bahncard50 costs are the higher amount, the banking statement that I sent them must be of something else.
I was like... alright, no sense in arguing with them anymore.
To me it's more telling of German mentality: if I follow all the rules, then the outcome has to be correct. Tell them it's not the case, and they won't know what to do now.
I once bought a laptop at Office Depot that had some kind of discount price, then decided I didn't like the camera. When I went to return it, they refunded more than I originally paid. I also pointed this out and they said not to worry about it.
Oh, actually it started with incompetence, too: I wanted to order the BahnCard25 but payment didn't went through (and thus, I did not finish the order process). When I tried again, the coupon that I wanted to use for the Bahncard25 was exhausted. (which is why I went for BahnCard50 afterwards)
And why did I cancel the subscription anyway? Because the trip that I planned (Hamburg to Paris) and that was listed as buyable was of course everything but buyable. Always failed at the last step of ordering with some indistinct error message. Well, they really did not want my money, that much I can say.
I was like... alright, no sense in arguing with them anymore.