I flew with Korean air out of JFK N.Y. they just asked for my Visa and I showed it to him with no problem. I come here every 3 months and depending on airline some don't even ask. I'm here twice a year for 90 days each time
I just left JFK and was asked by the airline to show my 60 visa which I did and even though my return flight was in 90 days there wasn't a problem my visa it stated I can extend for 30 days in Thailand
Cash, use your credit card when you can as long as you have a card that doesn't change extra for international transactions. Also try to have direct payment on your card to pay every month automatically.