I did some poor chicken math when I brought my chicks home in May, and I need to round up my flock by three. There are some 6-month old chickens for sale on Craigslist right now, and I'm thinking of getting three. My question- I am worried about introducing disease into my disease-free coop and yard, and I'm wondering what I should look for to avoid issues. I will pick the chickens up at the seller's house, so I will look for general cleanliness, but what else would be an indication of unwell chickens? Thanks!