Whenever you get Crystals in battle, put them in an auction for about 100 gil each. You will make good money this way, or you can put them in your bazaar for about 50 gil each.
At 6:00 in upper San 'Doria, the Wood Guild opens. There, you can by Arrowwood Lumber for 7 gil each. They sell for approximately 100 to 150 gil each. Also, the Luaun Lumber makes a profit, but not as much.
This trick requires three party members in Bastok. Behind the lighthouse in South Gustaberg is a bush labeled as "???". There, you can trade a Quus to have Bubbly Bernie spawn. He is not very difficult to defeat and drops a Steam Clock. If you set the second person to Quartermaster and make him wait at the entrance to Bastok Mines, he can run into the auction house and send it to the third person, waiting at the Mog House in Bastok Markets. The third person should take the clock to Malene in the very northern part of the town. She will give you 500 gil per clock. You can repeat this as many times as desired. Note: You can only hold one clock at a time, but you can have as many as you desired inside your delivery box.