There's oftentimes a significant variation in the lines even from one online sportsbook to another at any given moment depending on line movement. Are you saying that the exchanges are routinely better priced compared to 5Dimes, Bookmaker or other major books? Doesn't appear to consistently be the case from what I have seen. Also I wouldn't want to depend on gambling for a living but it seems pretty easy to get at least a few thousand bucks on the major fights just using a few multiple online sportsbooks.
the exchanges have much better value on all big sports almost all the time. however when we talk about a sport like mma which is still niche in europe where all the exchanges are and most of the customer base is located, so the lack of liquidity seeded into the markets leaves huge gaps in between prices wanted and prices offered, making big bets harder to get on the exchange for mma unless it's a big big fight and fairly close to the fight taking place.
But if we look at the prices for a random upcoming football match for example we can easily see why exchanges are a lot better value than a bookmaker. I went to oddschecker to pick a random one : man city vs real madrid this week we can see the exchange prices(at the time of writing this) are:
man city: 3.05 (+205)
draw: 3.55(+255)
real madrid: 2.54 (+154)
you can check pretty much any bookie, I randomly chose sportsbook.ag I see the odds are:
man city: 2.90 (+190)
draw: 3.5 (+250)
real madrid: 2.35 (+135)
so a £100 bet on real madrid would net you £146.3 profit on the exchange. not £154 because exchanges charge a commission on winning bets, in betfair's case it's the highest at 5% which is £7.70 hence the £146.3.
Yet the same £100 bet on the bookmaker would net you just £135 profit. If you then bet on say a hundred matches a year like many do, the difference would be over a £1000 so you can see it really starts to add up.
99%+ of gamblers will lose money, probably more, and the casual's will bet on who they think will win or who they support, blindly taking whatever price the bookie is offering. the above example is typical of the price differences but it's very common to see much bigger differences when comparing the odds.
the differences don't end there though. I'm not sure about a lot US books as much, but for successful gamblers like ITT, limitations on your max stake and sometimes even outright account closure on multiple bookmakers can become pretty common on Euro and other books, and not because you win...they couldn't care less if you win or lose because your bet has already been "hedged" for lack of a better term by them, offsetting their liability on your bet with the thousands of others they take on the other selections on that market.
Mainly it's because sharper gamblers consistently take better value lines time and time again, this is a big part of being profitable as you guys know. yet when you take value prices you are directly cutting into their profit margins when they are balancing their book.
Exchanges let you bet peer to peer with other gamblers and will NEVER limit you or outright ban you as they would stand to lose money from the loss of commission, NOT from the actual line itself like a bookmaker who will often take an extortionate amount of value out of the line to line their pockets. they get away with it because most punters don't understand odds or value that well, or many have never even heard of a betting exchange. also there's a distinct lack of governing laws in most countries to prohibit bookie's effectively banning sharps and only letting losing bettors and gambling addicts to bet with them.
Then we look at the key feature of the exchange, being the ability to bet against an outcome happening, known as "a lay bet". This gives you the possibility to trade your stake for an adjustable guaranteed profit or loss depending and the odds movement. and because betfair take commission this means the lines don't have value taken out of them like a bookie, this makes their lines correct when you work out the implied probability on each side. for example a hypothetical title fight:
Fighter A: 2.45 (+145)
Fighter B: 1.69 (-145)
This is an invaluable resource for gamblers, as a person who wanted to hedge fighter A with as lay bet, would have to stake more money to hedge it on a bookie than they would on the exchange due to the price difference, Again adding up to a significant amount over a longer period of time over numerous events.
sorry for the wall of text!
EDIT: i fell asleep ages ago writing this and just woke up lol, goddamn UFC's fucking with my sleep cycle.. so the prices in the 1st example I used have slightly changed by this time.