Tit for tat!
or
Buyer gets bought
or
Equivalent retaliation
or
An eye for an eye

if you have no idea what I am talking about, check this and this and this (in that order)

Thought provoking quotes.....1

I studied everything but never topped, But today the toppers of best universities are my employees - Bill Gates

Humor is merely tragedy standing on its head with its pants torn.

And there goes my favorite....
Never Argue With an Idiot Because First he will take you to his level & then he will defeat you with his experience