It is a common knowledge that it's a good idea to create a network of buyers / investors when one does wholesaling, in advance. So that when a wholesaler has a property to assign or to sell, he/she doesn't have to waste time when the time is of the essence, and the whole transaction is on the line.
It also has been suggested that a wholesaler needs to be sure that his buyers are what they say they are, in terms of their ability to close, i.e. their finances, credit, etc.

Question:
When the wholesalers first create that network of buyers / investors, HOW TO CONFIRM THE PROSPECTIVE BUYERS' FINANCIAL CAPABILITIES?
I mean confirm INDEPENDENTLY, since simple asking doesn't do it.

Note: We are discussing buyers / investors, NOT retail buyers.