> Merely listing prices (without an associated automated payment form which could imply a contract was en force upon successful payment) doesn't actually force you to do business with anyone.

In some cases it could. If you want to say "we categorically don't do X for ethical reasons", that can sometimes be more easily defensible in a way that "we have a standard price for doing this, but we don't want to do it for you in particular" may be harder to defend. (Even though I think both should always be possible.)