Go to the office and into the ledger. Select the inventory tab. Select a dinosaur to be sold at the auction. When your dino is removed for auction, go to the auction. Click on the "?" and then the "thumbs up." The old guy will bid on your dino. Repeat this until your selling price is high enough. Careful. Too much of a good thing can be bad.
Note: This trick only works on the older version of the game. (The one on 3 1/2" disks.)