I just got a phone call from a guy trying to persuade me to change my mobile phone provider. He asked if I was from England and when I said yes he started trying to speak English to me. Years ago that really used to piss me off... you speak perfectly fluent German to someone but they insist on speaking broken English back to you. These days I don't mind - it can be quite amusing.
Anyway, after he had made a couple of mistakes I suggested he should buy my book for Germans learning English! He then took down my web address and promised to have a look!
I doubt that it will lead to a sale but it was nice to turn the tables for once.