The tablet keeps dimming and locking between customers. Can the POS keep the screen on?

Yes. On the device open Settings from the selling screen or the Tables screen and go to Screen and sleep. Keep the screen on while the POS is open stops it dimming while the app is in front, and Never let this tablet sleep raises Android's own screen timeout to its longest once you allow the app to change that setting; a button opens Android's screen lock page if you want no lock at all. Sign out is on the selling screen, the Tables screen and Settings and takes the device back to the PIN screen. The POS and the counter tab in the docs covers screen and sleep.