That is a valid way to sort gamblers.  Many people are happy to bet money on propositions that have a negative rate of return.  That is the definition of a casino or a lottery.  The other type of gambling involves waiting until you have an advantage (greater than 50/50) before increasing the bet size.  This is what a very few blackjack players and many poker players are able to do.  They bet less when they don't have an advantage, and more when they do have an advantage.

So, you can best sort the people who gamble with odds that are above or below 50/50 just by observing the games they play.