Several things that may apply here:
First, it used to be that most credit card conversions from Belize dollars to US dollars used the conversion rate of 2 BZE to 1US. Now, however, most are using the conversion rate 1.97 to 1, or 1.98 to 1, based I think on the current interbank exchange rate (this is quoted in the Wall Street Journal every Monday in the World Value of the Dollar section). So things are costing a little more if you use a credit card.
This is odd in that as a practical matter the Belize dollar, due to a shortage of U.S. dollars in Belize, has actually DECLINED in value against the U.S. dollar of late, and some money changers are giving US$2.20 to $2.40 or more just to get US dollars.
Second, I believe that Banana Beach does have some kind of surcharge for credit card use. It's hard to figure because Banana Beach typically quotes inclusive rates, a rate that includes taxes and surcharges. I know that when I recently got a mailing from Banana Beach, in connection with a guidebook I am doing, it stated that the promotional rates quoted were inclusive of taxes and surcharges, whatever that means. (I would note, however, that these charges are small and that Banana Beach is a great value, one of the best on the island for what you get.)
Third, some credit card companies do charge a fee for converting any foreign currency charge. It is just another way a bank generates fee income.
--Lan Sluder
AmbergrisCaye.com 
