Ensure you are buying a happy healthy Parrotlet, ask your breeder questions, linage is extremely important. You don’t want to buy a bird too closely related or inbred. Also genetics play a huge part on the health. For example two of the worst possible combinations are Red eyed to Red eyed birds, this includes Ino and Fallow mutations as this can cause blindness in babies. I’ve had many emails regarding blind red eyed birds and this is more than likely due to improper pairings.