For an NBA game, I see a market for Spread and one for Winning Margin. The Spread market lists "Team A -5.5: 10/11". The Winning Margin markets lists "Team A, 6 points or more: 3/4". Shouldn't the odds for these two best be equal?
There's no fundamental reason they should be equal, because a bookies' job isn't to accurately reflect the chance of a team winning: it's to make as much money as possible for the bookie. If a bookie has taken too much money on one side of a line, they'll move the odds and/or the line to encourage punters to bet the other side of the line; bookies really don't like a situation where they're at risk of taking a significant loss if one result or another happens - their desired situation is if they have equal exposure on either result, and then they're guaranteed a nice profit thanks to their cut.