I play classical guitar. I really enjoy it; it's my golf.
I go through a set of strings several times a year, and I always use D'Addario Pro-Arte strings: they play nicely on my Alhambra 6P.
Something unusual happened at last string change: the set I bought had two Ds, but no A. I took a picture and posted a tweet about it, then ran out to the music store to buy another set.
When I got home, there was a reply from D'Addario offering to send two new sets of strings. I gave them my address, and they shipped them to me.
Thanks D'Addario! I appreciate it.