Related Clues:

• One takes payment for advice, of course
• I can tell you who will win — keep it dark — there's a row about it
• Adviser on betting
• One providing betting hints
• Betting pundit
• Seller of inside information
• Seller of information on racecourse etc
• One who sells betting advice
• Help in beating the odds
• He will have marked cards, of course
• Adviser of a sort
• Race predictor
• Race winner forecaster
• One giving better advice
• Supposed expert on horses from one end to another? Not quite