The Bookies apply a huge Over-Round to Correct Score Odds, and they also weight the Odds to ensure that betting a particular Score-Line "blind" (that is, applying the same Score-Line to all matches regardless of the likelihood of the outcome) will not make more money for the Bettor than is laid out. For example, the 2-0 Score-Line will on average come up about 9% of the time (it was 8.82% for 2011-2012, 8.16% for 2010-2011 and 9.19% for 2009-2010), and the "Fair Odds" for that would therefore be about 11.00. However, the average Odds on offer over ALL matches over the course of those 3 seasons just mentioned was only 10.11 (and where 2-0 was the actual result, the average of the Odds paid out was only 8.10)!
The only way to win big with Correct Scores betting is to treat it like you would Lottery, remembering that the chances of getting a 6-line combination win with low-score matches are more than 80 times greater than of landing a National Lottery Jackpot!