iPad -Secondhand

First, be aware that purchase of second-hand devices is fraught with risk - such as being sold a device which is Activation locked.

This user-tip, authored by one of the senior contributors, may help with understanding some of the significant risks associated with purchase of a previously used device:

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

If you do pursue this avenue, 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.

As for the iPad model that you choose, you would be best advised to only consider an iPad that is at least capable of running iPadOS 17.x - as this minimises the risk of encountering Apps that you wish to use that are not compatible with earlier versions of iPadOS.

For information, here is a full list of the highest version of iOS supported by the older and current models of iPad (for simplicity - “generations” are shortened to a number) that are restricted in their ability to be updated:

32-bit devices (obsolete)

iPad1 - iOS 5.1.1

iPad2, iPad3 and iPad mini1 - iOS 9.3.5 (WiFi Only models), iOS 9.3.6 (WiFi & Cellular)

iPad4 - iOS 10.3.3 (WiFi Only), iOS 10.3.4 (WiFi & Cellular)

64-bit devices

iPad Air1*, iPad mini2 and iPad mini3* - iOS 12.5.7

iPad Air2, iPad mini4 - iPadOS 15.8.2

iPad5, iPad Pro (9.7"/12.9" first generation) - iPadOS 16.7.7

(*) obsolete

Newer models are all able to be updated to the current version - iPadOS 17.4.1

• iPad Pro 12.9" (2nd generation and later)
• iPad Pro 11" (1st generation and later)
• iPad Pro 10.5"
• iPad Air (3rd generation and later)
• iPad (6th generation and later)
• iPad mini (5th generation and later)