That’s not at all the case here (VT). The local sellers are essentially all pasture-raised, free-range, etc., and their eggs are the only ones in stock. I have read some posts from them talking about the various ways they keep segments of the flocks separated, and they are being quite careful about any outside access.

Edit: I guess also the birds are indoors much more anyway, given the winter. It's 11 F here today, so probably they're huddled up inside :)