Some of you guys really need to bone up on the law....
Private sales are legal.
Buying and selling guns to make a profit is "dealing" whether or not you're making a living at it.
Selling a gun to an admitted felon or anyone else not eligible to own a firearm with prior knowledge of the buyers ineligibiltiy is a felony.
Selling a firearm to someone who is not a resident of your own state is a felony.
Example, you're at a gunshow and you buy a gun from a guy and then turn around the same show and try to sell that gun for a profit, you're "dealing" in firearms.
The "private sale" provision in the law is to allow residents of the same state to buy and sell firearms from each other for their own personal "use".
A legitimate "use" does not include buying it to sell at a profit. People engaged in business buy inventory to turn at a profit. This has held up in court every single time. There are dozens of guys doing time in the Federal big house for buying a gun and turning around and selling it at a profit.
Now the caveat to that is you buy a gun and months or years later it has appreciated in value and then you sell it at a fair market price, that's not a crime.
That's also why ATF will make several buys from someone before arresting them... they want to be sure that the guy is really "in business" and it's not just something that's happened once or twice.
Most of these guys have been "turned in" or informed on to begin with, usually by licensed dealers or someone they sold a gun to that was an unqualified buyer and got caught with it.
When I sell to a private party that I don't know, I always ask them if they're qualified to purchase the gun and get their address. It takes me off the hook.