we were in dalaman last year and were never asked too show our visas but we had copies of them if we needed to provide them,i reckon when you show your passport at security in dalaman it will show that youve aquired a visa.
Yes this has been the case for a long time, your passport shows the officer at passport control in Dalaman/Istanbul/Turkey in general, that you have a valid visa. How ever a short while back Turkey announced that you could no longer buy a visa at the turkish airport like you could before, so if you now arrive in Turkey without a valid visa you will be turned away and it will be the flight company who flew you out to get you back to your country of departure.
Soo Airlines, to avoid this hassle, cost, inconvenience are now starting to check if you have a valid visa BEFORE you get on the flight from UK.
IMHO, a VERY sensible thing to do, and i can't see an issue with this, as this falls into line with a lot of countries and their entry restrictions.