turnabout is fair play

Etymology
1755, British/Irish.

Proverb

 * 1) It is allowable to retaliate against an enemy's dirty tricks by using the same ones against them.
 * 2) * 1755,, The Life and Uncommon Adventures of Captain Dudley Bradstreet, S. Powell, Dublin, p. 216:
 * My Endeavours were used to perplex their Thoughts and Judgments; I told them, that at next Wednesday’s Dinner I hoped we would be informed who were to rule the Roast, that hitherto honest Men were kept from shuffling the Cards, because they would cast Knaves out from the Company of Kings, but we would make them know, Turn about was fair Play, and that two and three made five, though many Words did not fill a Bushel.
 * 1)  is morally right.
 * 1)  is morally right.