He doesn't say that though. He says "For a drink of your whiskey I'll give you some advice" You wouldn't want to hand over your whiskey unless you were getting a better deal than advice about gambling surely. I don't drink whiskey so maybe I'm wrong. Anyway the singer seems to have thought the advice was to be used in a broader sense.
We have a performer here - Martin Pearson - who does a pretty good parody of "The Gambler" (just how do you do italics by the way?) He thinks the old man got a good deal and that was the whole point anyway. Martin's song has the line "....for a drink of your whiskey I promise I'll get drunk..." More honest really.