Unless you're talking about a double chance method that's different than hedging your bets, such as on sports betting, there's nothing scammy about using it. I don't see how this method would work on gambling sites, though.

Either way, it sounds like OP found an exploit, which is scammy to sell to others. While it's not really illegal, I'm sure, it's still highly frowned upon, and I hope that whoever buys this method really considers what it is that they're doing.