The Scarlet is the macaw people picture when they picture a macaw, and it has a reputation among keepers for being the most demanding of the large ones - more reactive, more easily wound up, and less forgiving of inconsistent handling than a Blue and Gold or a Green Wing. Experienced macaw people often rate them the most rewarding for exactly the same reasons.
Make sure it is a Scarlet
Macaw hybrids are common, they are often beautiful, and several crosses involve a Scarlet parent and look close to one. A hybrid is a perfectly good bird to own, but it is not the same thing you are paying for, and it cannot be bred as a Scarlet. Ask directly what both parents were, ask to see them if they are on site, and treat a vague answer as the answer. Birds described as a Scarlet in the heading with a cross mentioned somewhere further down are worth a second look.
Temperament
Scarlets are intelligent, quick to bore, and more inclined than other macaws to escalate when something annoys them. They respond extremely well to consistency and extremely badly to a household where the rules change depending on who is handling them. This is a species where everybody in the house needs to behave the same way around the bird.
The noise and the beak
Both are large-macaw standard, which is to say considerable. A call that carries across a neighbourhood, and a beak that can break a finger. Neither is a reason not to keep one; both are reasons to plan the household around the bird rather than hope.
Fifty to sixty years
As with every large macaw: the bird will probably outlive the buyer. Arrange who takes it, write it down, tell them. It is the most commonly skipped step and the most common reason a mature macaw needs rehoming.
Feeding
A pelleted base with vegetables and nuts in measured amounts rather than free. Scarlets are active birds and need the calories, but nuts are still the easy way to make a macaw fat.
What they give back
Keepers who get on with Scarlets describe a bird that is more switched on than anything else they have kept - quick to learn, quick to read a mood, playful well into old age, and spectacular to look at from across a room. They are not a first parrot and they are not a quiet one, but for somebody who has done the work with other macaws they are often the last bird they buy.
Buying one
Ask about both parents. Ask to handle the bird, and have somebody other than the breeder handle it too. Ask when it weaned and about disease testing. Around a hundred breeders have listed Scarlet Macaws here, which is enough to be choosy. The breeders listed on this page raise Scarlet Macaws and can be contacted directly through the site.