I played my first hacker tonight. He (un)convincingly had a million wins and no losses and from the go he was shooting me with red shells. He still sucked and dropped out before the end.
But on topic, I often find that when playing an opponent who you can't lose it is best to let them think they are winning and get all the good boxes: red shells, boosts, etc.
Hold onto your best one in the last lap, and use it just before the finish. Works a treat.
The theory is - if you sit up front, you're more of a target and get worse items. Hang back and play it cool then catch them off guard.
It's not cheating - just smart.