said by plencnerb:
You as the "owner" of the WiFi device, go into your logs, and pull up all the info on who was connected to the WiFi device (or, your network as a whole) at the time. Then, doing research on every system, you verify what action was taking place at the time of the event, to see if the activity matches.
There's no law which:
a) prohibits you from doing a factory reset on your router any time you (or Starbucks) wants to.
b) there is no law which requires you (or Starbucks) to keep a log of all MAC address which have connected to your router.
c) there is no law against you changing the MAC address of your device at any time of your choosing.