If you
knowingly purchase stolen goods, you are guilty of a crime. If the seller swears the goods aren't stolen and even signs a contract to that effect, you aren't guilty of a crime
unless you know that the goods actually are stolen. They key element is the intent to buy goods that have been stolen; merely intending to buy goods is not enough.
More appropriate examples would be Napster or Limewire. Their TOS's barred using their programs for illegal ends, but both companies actively promoted illegal downloading. In the end, liability issues brought down both companies.
IAAL. Please don't armchair lawyer, or you'll end up like the guy who runs TechDirt.