Had a look at the odds on offer at the moment, then got distracted by the margins for the outright markets
Nitrogensports = ~3%
Cloudbet = ~5%
Sportsbet.io = ~8%
Why are some much bigger than the others?
Odds on books adjust up/down depending on individual betting volume.
Its identical to crypto exchanges offering different prices on bitcoin / alts depending on user demographics, regional demand, etc.
Nitrogensports 3% could mean it has the highest betting volume out of all 3 books. Cloudbet @ 5% could mean its betting volume ranks 2nd. Sportsbet.io at 8% could mean it has the lowest betting volume out of all 3 books. The book with the highest betting volume would probably be the most accurate representation for the same reasons poll data tracks towards being more accurate the higher the number of total people polled.
With the high number of variables and intangibles present in sports, its difficult to gauge the size of someone's heart, how badly they want to win. Its difficult to put a number on the amount of preparation someone has invested into a fight. So of course, accuracy is an ambiguous topic as far as betting odds go. Odds are like poll data, they can mimic public opinion. Books also have insider info a lot of the time which trends towards the empirical. Odds swings are like poll data though.