There are many reason why Macaws with either bluff or bite, Most times are due to hormones. I do not agree with some posts, it is very important for you to remain the Alfa in your relationship with your Macaw. Think of it this way, most macaws are like 4 year old children who test you every chance they get, it is completely up to you on how you respond, do you give into them and allow an action to happen, if so, you cannot blame the Macaw on an unwanted action, if you try your best to stay in control, most cases, you win and the Macaw soon learns just how far they can push you.
Biting should never be allowed or laugh when they try to bite you, this action needs to be taken at once, Macaws who bite need time outs just like children, I either return the Macaw to their cage for a 5 minute time out or until they have calm down, sometimes I cover their cage with a blanket for 5 min at a time.
Once they calm down and allow you to hold, pet, or have them step up, just like children in a candy isle, it's time to reward them and tell them how good they are to have stepped up, no bite, or allow you to pet them.
Another bit of advise here with Macaws who like to bite, have their favorite toy with you, if they try to bite you, allow them to bite the toy instead, this teaches the Macaw that it is just fine to bite the toy but no okay for them to bite you. Best of luck Joe