Amazons as a family (Amazona species) require DNA Sex Testing!
Yes, there are some possible indicators, but they are little more that a 50/50 guess.
Remember that Amazons, yes all of them, are designated as endangered and fall under the guidelines of CITES regulations, which require that the seller provide a detailed Hatch Certificate along with a Bill of Sale. The Hatch Certificate should have the Species of both parents, the Hatch Date, Name and Contact information of the Breeder and any other sellers between the Breeder and you. NOTE: Most Breeders provide a DNA Sex Test document! Important: You want the original document, not a copy!!!
Assure that your baby is 'fully' weaned and has been on solid food for at least two weeks!!!
NOTE: Most seller warrantees require that you have your Amazon Vet Checked within two weeks of taking your Parrot home. IMHO, take your Parrot directly to your Avian Professional the same day you get your Amazon! Also, take your document set (as defined above) to your Avian Professional so that they can copy it and add it to your Babies Medical File!