Taking a couple of mintues observing the bird and looking for indications of a healthy bird can save you hundreds on dollars on vet bills.

Before you buy a bird, observe the bird of interest for a while. Check to see that he does not have any excretion around his eyes, nostrils, and vent. Note that if the feathers around his vent are stained, it may be indication that the bird is suffering from diarrhea which can be caused by an array of bacteria or viruses. However, if you see normal droppings stuck around the feathers of the vent, this does not indicate an ill bird. When birds are young, they have not learned how to pull up their tail when excreting feces and because of this, the feces gets stuck on the feathers immediately near the vent.

His feathers should be smooth and slick, indicating that he maintains himself. Healthy birds are constantly grooming to ensure that their plumage is clean from debris and in top notch condition so that if they are surprised by predators, they can make a hasty escape. A bird with dirtied ruffled feathers indicate an ill bird. Observe to see if he has any bald spots, an indication of plucking. Be cautious if he is fluffed up, it is a sign that he is either sick, getting ready to groom himself, or is sleeping/has just woken up.

Look out for activity; an active and vocal bird is most likely a healthy bird. Watch how he interacts with the other birds (it gives insight on his temperament). Check to see that he has four toes: two pointing forward and two pointing back (missing toes do not suggest an unhealthy bird but rather a physically flawed bird).