As for keeping people off of the property for sales, I would band each bird individually so you can tell that they are all different, then take multiple photos of each bird, trying to get the bands in the image as much as possible, then have a meeting place nearby, maybe a store parking lot, where you can exchange the bird and money without them being on the property. It might help to have the bird in a wire cage as well so they can see the birds that they are buying and confirm that it is the same bird that they saw photos of. That in addition to documentation showing hatch date, and any other information you know about THAT bird or at least that group would help make the sale.