Exchanges

Exchanges (Novig, ProphetX, Kalshi, Polymarket) are not sportsbooks. A book posts prices for both sides of the market. An exchange matches you with another person or bot that wants to take the opposite side of your bet.

That difference matters for both betting exchange prices and devigging against them.

Where the liquidity comes from

Most of the money on an exchange is not casual bettors. It is market makers: traders and bots that sit on both sides of a market, and update faster than most books.

That is why a fat +EV flag on an exchange can be a sharp trap:

  • A lone offer on a thin market is often someone who knows more than the sportsbooks (injury, lineup, weather, insider info, or just a better model).
  • The scanner will still treat that price as a real number. It does not know why the liquidity is there.

Thin, one-sided liquidity is the warning sign. If only one side has size, or the size is tiny, do not treat the number as fair — and think twice before betting it. See Trusting +EV signals.

When to trust exchanges as devig books

Exchanges can be excellent fair-line sources. The same market makers who trap thin markets also produce some of the sharpest consensus prices in sports when the book is healthy.

Trust the exchange more when:

  • There is high liquidity on both sides.
  • The vig is tight. A small gap between the two sides (think something like −105 / −105, not −130 / +110) means makers are competing and the midpoint is a serious estimate of fair.
  • The market is popular. Main NBA / NFL / MLB lines and big props are cleaner than obscure alts.

In that state, weighting Novig, ProphetX, or a prediction market in Devig Books is reasonable — same idea as leaning on Pinnacle or Circa.

Use Min Liquidity on the +EV Scanner so thin exchange quotes never enter the fair line or show up as plays. If you only want exchanges as devig sources, keep their weight modest unless both-sided size is the norm for that sport.

Fees

Exchanges often have a fee on top of the price — commission on winnings, a taker fee, or both. EVantage's EV scanner does not account for these fees.

Build that into the decision: either require a higher EV% on exchanges, or skip the play if the net number is no longer +EV.

Key takeaways

  • Exchange liquidity is mostly market makers. A juicy one-sided offer can be a trap, not a gift.
  • Trust an exchange to devig when both sides have size and the vig is tight.
  • Scanner EV is pre-fee. Commission can turn a small plus into a minus.