I bought an old iPhone 5c at a yard sale, and it has an iCloud lock on it...any way to get it off?

Hello ~ No…unless you can take it back to the person who sold it to you and they can or will remove the lock. We cannot help and neither will Apple. Take a look here:

Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Also:

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

~Katana-San~

You may have to work with the previous owner to remove the lock.

How to remove Activation Lock - Apple Support

No. Recycle the phone responsibly, unless you can find the person who enabled the Activation Lock theft deterrent feature.

Hello ~ The key in this situation may be finding the previous owner and buying it at a yard sale …well that may not be possible.

~Katana-San~