Resetting iPads

To erase/reset an old iPad before trading in, go to Settings > General > Transfer or Reset [device] > Erase All Content and Settings. This will completely erase the device, including any credit or debit cards added for Apple Pay, photos, contacts, music, or apps. If Find My [device] is turned off then Activation Lock will also be turned off.

Prior to trade-in, you should properly prepare the iPad. This support page provides full guidance:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support