As well-detailed as Dragoner28's guide is, I'm pretty sure this solution will allow you to easily defeat the Dealer with virtually no effort whatsoever.
Just progress through the levels like you normally would, but when you get into the three-block stretch right before the boss, make sure of two things. One, make sure you are afflicted with Midas Appetite, a curse that causes you to eat gold instead of food. Second, make sure you either found or purchased the Emergency Ring, which gives you a free resurrection at the cost of all your food. If you're missing either of these, just forfeit and try again until you have both.
I'm not sure if it's a glitch or what, but as long as you have both of these things in effect, you become invincible during actual combat. In my case, I reached the Dealer with 56 gold left over, and every time my health depleted, it just reset back to 56 health infinitely. I actually went back and re-tested this; the second time I got there I just left my controller sitting there, came back half an hour later, and the fight was still in progress.
Hopefully, this alternative method will work for anybody who's having trouble beating the Dealer legitimately.