I bought an iPad at a garage sale.

Thriftingmomma wrote:

I bought an iPad at a garage sale. The person who would belong to had passed away. I have no way of finding the Apple ID or password. What can I do to unlock it

Ask the family from whom you bought it for help. You may not know the Apple ID – but they hopefully will, even though they might not know the associated password.

You say that the original owner has passed away. In that case, the Administrator or Executor of the estate could make a request to Apple to remove the Activation Lock and reset the device. Apple will require, and verify, legal documentation – such a death certificate and a court order, so don't even think of making the request yourself.

Here's information that might of interest to the seller:

How to request access to a deceased family member's Apple account - Apple Support

As LotusPilot said, a seller should also properly reset an iPad for its new owner:

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

If you can contact the family. and they can do these things for you, you will be able to set up the iPad as if you had purchased it new. If you cannot obtain the help of the family, and they cannot convince Apple to remove Activation Lock, the iPad will forever remain a "brick".

The All Too Common SAD Reality of Buying a Used iPad/iPhone – Apple Community

If the iPad disabled or Activation Locked, unless you can independently obtain assistance from the previous owner (clearly not a viable option), the iPad is (and will remain) useless to you. If you were able to contact the original owner, they would have required this information:

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

Here are the Apple support pages that outline the Activation Lock - and the only mechanisms by which it can be satisfied:

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, you’ll not be able to defeat or bypass the Activation Lock. With documentary evidence that you are the original owner (such as the original sales receipt showing the serial number), Apple may be prepared to assist - otherwise they and nobody here will be able to help you.

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.