Never exchange more than 50 dollars from airport and another thing you can take BTS train , in 100 baht you will be in Sukhumvit or any other area of Bangkok. Once you reach your hotel you can exchange your money from Superrich or other official banks of Thailand, you can get best rate.
if you are carrying dual citizenship then also one country can deny your entry if you are found suspicious. In Brazil many people have Italian passport just because of their great grandparents they never been there , sometimes it can create problems also.