How can I determine if an iPad is stolen?

Here is what Apple suggests when purchasing a previously used device:

Check for Activation Lock before you buy a device from someone else

Before you buy an iPhone, iPad, or iPod touch, from someone other than Apple or an authorized Apple reseller, make sure that the device is erased and no longer linked to the previous owner’s account. Follow these steps to check if the device is ready to use: 

1. Turn on and unlock the device. 
2. If the passcode lock screen or the Home screen appears, the device hasn't been erased. Ask the seller to completely erase the device by going to Settings > General > Reset > Erase All Content and Settings. Don't take ownership of any used iPhone, iPad, or iPod touch until it's been erased.
3. Begin the device setup process.
4. If you're asked for the previous owner’s Apple ID and password, the device is still linked to their account. Hand the device back to the seller and ask them to enter their password. If the previous owner isn't present, contact them as soon as possible and ask them to use a browser to remove the device from their account. Don't take ownership of any used iPhone, iPad, or iPod touch until it has been removed from the previous owner’s account.

You will know that a device is ready for you to use when you're asked to "Set up your iPhone," “Set up your iPad," or “Set up your iPod” the first time you turn it on.

This article, authored by one of our senior contributors, highlights the many risks associated with purchasing a pre-owned device:

The All Too Common SAD Reality of Buying … - Apple Community

In summary, you would be well advised to only purchase a pre-owned device from a reputable source - perhaps, by example, a reconditioned device sold directly by Apple - or someone known to you that you trust. Consider avoiding sources such as FaceBook Marketplace and ebay - as these are platforms are commonly used to pass-on stolen goods.

no, you can't track or check theft information by serial numbers on apple devices

Can I check if an iPad is stolen before p… - Apple Community