Couple of things that you should look for if buying from an unknown breeder. Birds should be active! If the bird is lethargic do not buy, example: if my kids are helping me in the pens and they can walk over and just catch one real easy, I look for a problem with the bird. Now some birds are very friendly, but ask to hand feed them if they are so easy to catch, use bread, cat food, or grains. If they eat then they are probably OK. Lift the bird up if possible (wear gloves). If the bird has no weight then something could be wrong. Feel the breast muscle, although not large like a chicken or eating bird, you should be able to feel muscle and not just bone. I lift my birds from time to time just to check them. Peafowl can be prone to sinus infections in certain conditions and this will result in a swollen side of the face. Do not buy them due to your needing to medically treat them as soon as you get them. Now lancing a birds eye is the last, last resort for the sinus infections, NEVER buy that bird at auction, but the post is not about treatment so.... I would hesitate to buy birds that ran directly with chickens, seller can have chickens, but they should have a physical separation. At auctions it is trickier, look at the mood of the bird, it should be active and on alert with so much going on around it. The bird with the closed eyes, ruffled feathers and crouched down look is the bird not to but. Its always a risk, but its a judgment call. Quarantine the bird once you get it so that any disease or problem can become evident before placing it in with your flock. This will prevent spread of any carried disease to your flock. NPIP breeders have annual testing of their flock for certain diseases, pullorium, avian influenza etc.. so this may give some credibility, but don't rely solely on this.