I will share my experience.
Aware of the risk, I purchased a used Meraki MR at auction.
Device was already registered and not available.
The seller was not the rightful owner.
They obtained the Meraki device from somewhere and sold them at auction.
Therefore, the Meraki device remains unusable because the rightful owner cannot be contacted.
A self-protection measure is to contact support prior to purchase to ensure that the serial number is unregistered.
Of course, you will need to obtain serial number information before doing so.