1. Activity Level
Look for a bird that is active and alert, and interested in what is going on. Younger birds often sleep more than adults, but still usually wake up and are interested in new people and activity around their cage. Avoid birds that are puffed up, sleepy, or reluctant to move (signs of illness).
Should be clear and bright, with no discharge or swelling.
Should be clear of discharge or blockages. Scaliness around the nostrils can indicate a mite infestation.
The top and bottom parts of the beak should meet evenly, without gaps, and in good alignment. The top part of the beak should not be overgrown or overly pointy, and the edges of the beak should be smooth.
Look for birds that have shiny, healthy-looking feathers with no downy feathers showing through. There should be no bald spots, except in Lutino cockatiels which often have a bald spot behind the crest. Baby birds take a while to become fully feathered but by the time they are weaned they should have all their feathers and are not fluffy anymore. However, young birds often have frayed feathers and a bit of a dishevelled appearance.
In young birds, the feet should be smooth and soft, while in older birds they are usually a bit more scaly in appearance. However, watch for overly scaly feet which can be a sign of problems. The feet shoulb be free of bumps or sores.
The vent is the area around the combined opening of the urinary, digestive, and reproductive systems (just in front of the tail on the underside of the bird). This area should be clean and dry, free of matted feathers or fecal material.
8. Body Condition
This is a bit more difficult to assess since you need to be able to feel the chest of the bird. Get the seller to hold the bird on its back, and try to feel the keel bone, which is a long, thin, flat bone that protrudes from the chest wall (breast bone) of the bird and runs down the midline of the bird from the chest to the belly. In a bird in good condition, the keel can be felt but its edge is nearly even with the muscles on the chest. In an underweight bird, the keel bone is very prominent and in an obese bird it is very difficult to feel. You want a bird that is in good condition and not too skinny (although newly weaned birds are often a bit thin) or too fat. More detail on feeling the keel is available in "How Do I Assess a Bird's Body Condition?"
Should be regular, quiet and not strained. Wheezing, clicking, shorting, or heavy, laboured breathing can be a sign of respiratory problems.
10. Attitude to People
This is not so much a health issue but gives you an idea of how the bird relates to people, which is important in determining what kind of pet it will be. Ask to handle the bird. Ideally, look for a bird that is very social, readily coming to you and staying calm throughout handling. A bird that initially resists a bit but warms up to you also has potential. A bird that panics when you try to handle it and bites or shrieks is probably not a good pick.