True, but as we've seen with our only impeached President, pardons are not always "free." They can be bought.
Mercy is a free pardon; we have been acquitted by God's grace alone through Jesus Christ taking on the punishment rightly due us and paying for our sins in full.
Free of charge. No payment required. Only gratitude, after the fact.
This would imply that God can be 'bought.' If that's how the Protestants understand God's integrity, it would be the ultimate in anthropomorphism.
It's not a gift one gets for a birthday or at graduation. It has no chance of being corrupt by the Giver. It is priceless (nothing in the world can buy it, earn it, deserve it). There is no need whatsoever to call it free, or a gift. In fact, it's just plain wrong and misleading.