Ok here's a new one:

Each Friday- a stranger calls Tom with a hot tip for Saturday's race. Each week for three weeks the horse wins. Tom is being conned. How?

Clue 1: The phone call comes the day before the race.

Clue 2: On week four- the stranger asks for money before giving his tip.

Clue 3: Each race has seven horses entered- and Tom's previous wins were luck.

Clue 4: The stranger began his con game by calling 343 different people.