Good point. I'm looking into it right now. At the moment, I think the solution is to consider the estimated odds being displayed at the time of betting. Since, that is the odds that made the bettor place a bet on that event. I will talk to everyone who's betting on freebitco.in and see what they think of it.
Estimated odds on freebitcoin are based on the current amounts placed on the outcomes by the bettors and not on the likeliness of the outcomes to occur as for classical bookies. That means, you can get estimated odds at 2.5 while on all other sportsbooks the odds for the same outcomes will be 1.5 for example. So it would be very easy for freebitcoin players to chose the overvalued "estimated odds".
It will ultimately even out, if you get the estimated odds at 2.5 while it is 1.5 on classical bookie, You deserve to be rewarded. generally speaking, such huge disparities are rare and any advantageous spot for a gambler is evened out by bettors(unless some huge bet is made on an underdog). I have registered on freebitco.in, just to see how it works. From what I have found up until now, for popular soccer matches, I have actually found worse odds on Freebitco.in for at least 2 out of 3 outcomes(if not all 3). So, I do not mind the screenshot posted with whatever odds one gets at the time of betting. It cant be too far off than the actual odds provided from other sportsbooks.