In wholesaling it is extremely important to find motivated sellers. If they would rather list it with an agent than chances are they are not to the point where they are motivated enough to sell yet.
On the other hand there are different ways to wholesale deals. By this I mean that it does not always have to be an all cash sale. Make sure you ask the fsbo's whether they would consider having you take over their payments or if they might be willing to do some owner financing. If they say yes to either one of these you can find another investor to help negotiate the deal for you and they can pay you a finders fee.
The bottom line is basically to make sure you are asking why they are selling and when do they need to sell by. This will tell you what their motivation level is.
Best of luck!
Michelle