Funny that, same here too - and as Dave said, friends who were staying with us experienced the very same thing.
I'd exchange my money with anyone but this guy. What a lovely way to treat returning loyalty, GIT!
Finans Bank is probably best - you don't need to bank there to change sterling, also Dikmen (yellow change shop on the corner before Finans, and if in Calis and you need to change money there, the guy in Onur Silver shop (opposite Maria's Bar) is the only guy I would go to.
Scunner