I think it's been mentioned a couple times (possibly by Harry) that there can be and are wizards who use their magic to make a crapload of money in ways that might be stretching legality or ethics in the mortal world. Buying and selling information, using magic to stack the odds at a casino, summoning demons for lottery numbers, etc.

So long as you're not breaking the Laws of Magic, the White Council doesn't care one bit what else you're doing with your magic. Harry's perpetual near poverty is mostly self-flagellation on his part. Case in point -- he could've made a mint signing on with Marcone.