When you find Yojimbo, wait for him to make his offer. After he makes the offer, which I believe is 300,000 gil, offer him half of what he wants plus 1 gil. He will then lower his asking price. Increase your offer by 1 gil, which will force him to lower it again. This time, he will not take any amount much lower, so offer him about 5-10,000 gil less than what he wants, generally around 190,000, and he should take it. If not, repeat the process and simply offer a little more than your previous offer. If you offer him TRIPLE what he wants at any time, you not only gain Yojimbo, but he gives you 2 Teleport Spheres as well.