"Oh dang, you ticked the 'not a robot' box but you are actually a robot ... Ah, no worries, I'll put a call in to head office, get the paperwork changed. Well, enjoy your car! ... And don't forget to come back in six months for your free oil change! ... for the car, I mean."
You may sell to someone represented by a robot, but you're not selling to the robot.
When using a vending machine, your making a trade with the vending machine company, not the machine itself.
The closest thing would probably trades with wild animals. Are there any laws on that? (Probably not, but the situation is not unthinkable.)