I'm so glad you raised this post Jeff McDermott. IMHO, I think the hardest part is the mindset of the wholesaler. It should be treated as a business and not a hobby. It needs consistent action in every single part. Two factors are the number of hours one is willing to spend every day and one's monthly budget for prospecting.
The second hardest part is MARKETING - for both sellers and buyers - that of course depends on consistency and the market demographics. In a market where new businesses are opening and old ones booming, finding buyers may be easier and vice versa.
Finally, the mindset of the general populace also plays into it. An open-minded city is a perfect breeding ground for wholesaling success. On the flip side, if you operate in a market where the "real estate professionals" are stuck in their old ways, homeowners won't even look your way even if you offered them 200% x ARV! I've heard both sellers and realtors say "My realtor says it's illegal", "Hey, you can't do that here!", "I'm gonna take this to the Attorney General, you a@%#&!e" LOL
But there's one thing that trumps all these challenges - a fanatical hunger for success (which most of us don't really have)
Just my two cents! LOL