Professional mode
Select arcade mode, then highlight the "Hard" selection on the difficulty selection screen. Hold L1 + R1 until it changes to "Professional".

Hint: Saving money
Do not waste money on upgrading the first few cars you have in the game. Instead, practice being a better driver. Wait until you win a car with some real potential until you upgrade. For example, start out with a Mazda Miata, but do not upgrade. Use it to win a Mazda RX-7 Effini 3, then upgrade.

Hint: Easy money with memory card
Two memory cards are required for this trick. After you have earned about 200,000 credits, purchase a car, such as the Mitsubishi 3000 GT. Upgrade it up to the max. This will leave you almost broke. Go home and save this car memory slot two, then return to the title screen and load your last game from memory slot one. This will give you your money back, and you can now go home and trade from memory slot two. That car that you just spent all those credits on will only cost you retail price.

Hint: Free tuning with memory card
Two memory cards are required for this trick. After getting some money or cars to sell, save your game to both cards. Then buy the car you want, tune it, and get all the tires. Save your game to the memory card two. Then, load the game from memory card one, go home, then go to trade. Load the memory card two's garage and buy the car you just tuned. Then, save the game to both cards. You have now bought a fully tuned car for the price of the stock car. Repeat this as many times as needed.

Hint: All four bonus cars with memory card
Use the following trick to get all four bonus cars and all colors after racing a series only one time. Two memory cards and enough money to buy all the cars at the resale price are required. Save to memory card one at the end of the second-to-last race with enough points to skip the last race. Skip the last race. Press X when the black circle is under the desired car. If you do not get the car you desire, reload card one and try again. Once the desired car is chosen, save to memory card two. Reload card one, skip the last race and choose the desired car. Go to trade without saving in the home menu. Load card two in the trade menu. Buy the previously chosen car, then overwrite and save to card two. Reload card one, skip the last race, choose the next car, then go to trade again. Load card two in trade. Next, buy all previously chosen cars, overwrite, and save to card two again. Repeat until all desired cars and colors have been acquired from only one series.