Are wholesalers useless?

[Steven Vaughn]

If finding good deals are so easy once you know how to market, then why do rehabbers pay wholesalers a finder's fee when they can just find a deal by themselves for more profit?
And even if I do find a really great deal and get it under contract, can't they just steal the deal from me by contacting the owner behind my back and setting up their own contract that is more appealing to the seller? If that's not possible because of my signed contract, then won't they at least try wait out my left over days for it to expire, and THEN set up their own?
I was just wondering.. because I feel like if experienced investors are tempted with a deal that has a VERY high ROI, they will try to take advantage of beginners like myself who have very little clue as to what they are doing. One of the reason why I haven't started is because I have a strong fear that I will be taken advantage of a lot!