Profits margins normally depend on the price of property you're dealing with, which corresponds to your market. If you're dealing mostly with $30,000 houses then I would expect $3-5K per deal. If you're dealing with mostly $100,000 houses then I would expect more like $8-10K per deal, $150,000-$200,000 houses I'd be looking in the $15K range per deal.
Yes, you can make, and I have personally made $20,000+ on smaller wholesale deals, but that's not the norm. My target is $3-5K in profit on a deal, and every once in awhile I will hit one out of the park.
I remember I had one house that would retail for about $75K and it needed 10K in repairs. It was a smaller house in a lower middle class area that has a fairly strong appeal for landlords and rehabbers. I had an investor that loved to carry notes in the area and I knew what his purchase numbers were. I asked the seller what he needed to get for the property and he told me $20,000. I told the seller we could work with that and I got a contract signed. My investor wrote me a check for $45,000 when I closed and I walked away with $25,000. He was happy and I was, too. :D
Does it happen every deal, NO. Does it happen every 20 or 30 deals, NO. But does it happen, YES. You focus on just hitting the ball, and every once in awhile one goes over the fence. That's the game.