Check the guides at: //AmbergrisCaye.com/fishing/
here's a few others that do it privately and don't have webpages, call them when you get to town...
Luis Caliz at 011-501-26-5025, great guide and fisherman.
George Bradley has a brother that guides spin fishing. I can't remember which brother it is, but you can reach George at 011-501-26-2179.
Nesto Gomez { a very good guide}-- one of the best tarpon and bonefish flyfisherman! He works out of El Pescador.
Omar Arceo, does a heck of a job.
For flat fishing call Eloy Gonzalez at 026-2337
Pedro (Pete) Graniel. First rate equipment, including boats, and does both offshore, reef and inshore (tarpon, etc.) Keeps his boat just south of town. Ask anyone how to contact him. He's well known.