we do work very similar to betfair.
The % is just a different representation of the odds. Instead of saying odds of 2.0 you could also say: 50% likelihood.
If you prefer the decimal odds (like betfair) or american odds you can change that (chose it on "options")
Since you are online let me ask another question which is ? I see Over 2.5 and under 2.5 goals for the same game Ajax vs Celta, why there are 2 options for Over 2.5 goals ON and 2 options AGAINST ? Shouldn't it be only 1 option, you bet against over 2.5 or you bet on over 2.5 ? It's a bit misleading for me.