When only eleven of 400 names on a high-end buyer list answer, is there a business yet

Verification is not a document problem. Ask what they bought last and what they paid, then go look at whether the recording matches what they told you. That works in the counties where sale prices are public. About a dozen states do not publish them at all, so there you are back to asking for a reference from the closing attorney or title company on their last deal. That is a normal request between professionals and nobody serious takes offense. On the 55 cents buyer: that is a real number for someone who intends to hold a distressed 2M house through a long renovation with no financing. He is pricing risk rather than parking capital. He is also the buyer who will still be there when the others go quiet, so keep him and stop hoping he moves.

In a market that tops out around 240k none of the dollar figures apply, but 11 out of 412 is exactly the ratio rural buyer lists produce too. The people who answer twice are the business. Everyone else is a name in a spreadsheet that makes you feel further along than you are.

Before you set a price on either version, find out whether what you're describing needs a license in your state. Getting paid to find a buyer for someone else's property is the sort of activity that can fall under brokerage depending on how your state defines it, and the fee-share version may look more like that than the retainer version does. I'm in the middle of the licensing process and the definitions are wider than I expected. Ask a real estate attorney in your state and get the answer in writing, because it changes which of your two options is even on the table.