Final Fantasy X Tips

O'aka XXIII, Merchant Extraordinaire!
The amount of gil you give to O'aka determines how much his prices differ from that of other shops.

0 - 100 Gil: 100% increase in prices
101 - 1,000 Gil: 50% increase in prices
1001 - 10,000 Gil: 20% increase in prices
10,001+ Gil: 30% discount on all prices

In other words, it will only cost you more to buy items from him until you give him at least 10,001 gil. When you do, you'll get a big discount. Furthermore, if you talk to him in Macalania Woods, near the area where you fight Spherimorph, you can convince him to lower his prices in that area by telling him that the prices are too high.