They shouldn't be runny nor should they show constipation. If they do seem a little runny, check the diet to see if they are on a pelleted diet. If so it MAY account for the runny looking poop, as birds will consume more liquids because the dry pellets make them thirsty. Check the color of the poop. Next take a look at the breathing, which should be even, easy, but quiet while the bird is at rest.
Labored breathing is a sign of illness.
You may want to check the birds breathing after exercise, or have someone else more familiar with the bird hold the bird and make it flap to see how it breathes after exercise. The bird should not be frightened, but if the bird is raised up then lowered, most likely the bird will flap. The respiration rate may quicken, but it should quickly return to normal. Listen for any wheezing sounds. The wings should fold evenly and close to the body and extend fully when opened.