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~

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

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

How to remove Activation Lock - Apple Support

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~