If locked/disabled, you can attempt to reset the iPad - however, you will more than likely trigger an Activation Lock which will render the iPad unusable to anyone other than the previous owner.
Disabled
If your iPad is disabled, or you have forgotten your iPad passcode, you’ll need to follow this process:
If you’ve forgotten the passcode on your iPad, or your iPad is disabled – Apple Support
You’ll need access to either a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS).
Activation Lock
Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be turned off:
Activation Lock for iPhone, iPad, and iPod touch - Apple Support
Turn off Activation Lock – Apple Support
As you will discover, unless you are the owner of the AppleID that was last used to activate the device, or unless you can secure the cooperation of the previous owner, you’ll not be able to defeat or bypass the Activation Lock. Without documentary evidence that you are the original owner (such as sales receipt showing the serial number), Apple won’t assist - and nobody here will be able to help you.
You proof of purchase from the Auction will not be accepted by Apple - as it proves nothing more than you not being the original owner.