Rl burnside said:
I think you need to familiarize yourself with the idiosyncrasies of a particular sport you're betting. I determine value by understanding the sport and the players competing then seeing how the line equates.
This will forever be a topic debate among bettors and everyone will have a different opinion. In my opinion, there are three types of bettors:
1) Model builders/Market followers
-Although these two probably shouldn't be in the same category since you have to be fairly intelligent to build an efficient model, and you don't have to be intelligent to just follow markets, the end result each bettor is hoping for is still the same. Both want to make (or find) an exact price on something, compare that price to what's available, and then maximize that edge via Kelly.
So if think something should be -150, they find -125, they plug 60% into their Kelly Calculator with -125 at the bet price and it tells them what percentage of their bankroll they should bet.
*A side note about Kelly is that it will often advise you bet huge sums of your roll, this is why many people use 1/4 Kelly or sometimes even less. When I am comparing the market I use about 1/5 Kelly.
2) Handicappers
-I think that's what a lot of people on here are trying to be. They research the game, look at trends, stats, etc, and determine in their opinion if a certain line has value or not. The difficult part is that this approach is extremely subjective. How do you know -130 has value? How do you know they're going to win at least 56.5% of the time and not only 54.1%? It seems small but the same difference (50% vs 52.4%) is the margin allowing books to make money and a vast majority of people to lose theirs. I do not think it's impossible to go about winning this way, but I'd strongly advise against doing anything but flat betting. You MAY be able to determine the black and white question of "Do I have an edge", but it's almost impossible to determine exactly how much of one you have which is needed in order to properly adjust your bet size.
3) Visual Bettors
-This would be casual bettors, or people who just watch hours on end of whatever sport they are betting on. I think it's nearly impossible to win this way but I do personally know one person who does this with CFB and has done very well.