There are things to think about before you buy it.
Do you have enough time to socialize him? they need 3 hours of out of cage time a day.
Will you neighbors be okay with the noise?
Are you able to care for him for the next 60 years?
Have you done research on the species?
Aside from that, look carefully at the shop. The bird should be on a pelleted diet with fresh fruits and vegetables. The cage must be clean. The bird looks in good heath, but check it's feet, eyes, nose, and feathers for anything unusual.
Let us know how things go!