These lenders will usually have a place of business that you can go to, have a website of some kind, have a professional email account that's not gmail, have a license or professional credentials of some kind, or have done verifiable loans to someone else I know.

Now if it were a commercial property with verifiable cap rate comps then EVERY property is a viable opportunity AT MARKET CAP RATE. 

My claim is easy to verify as you can look up the appreciation on San Diego real Estate for a wide range of years and compare the appreciation to other markets and compare just the appreciation to what could be expected in cash flow in a better cash flow locale. 

Would this be your only verifiable income?

You put in the $2500 and he gets it when the deal funds as verified by your closing attorney.

Once my client is completely ready to submit, I send over a full package to the other party including an the signed Purchase and Sale agreement, a copy of their pre-approval letter or proof of funds, a picture of the escrow deposit, a sheet explaining all of the comps that verify the offer price, and a brief explanation in the email as to what some of the terms are. 

It's a serious, serious waste of time and money (I'm being redundant here, I know)I've assigned slightly over 75 lease option deals in 10 different states, and not once have I ever spent a dime of money marketing my deals (okay, this might be a bit of a stretch, because I've spent money on local proxy IP's and local phone numbers to create a new craigslist phone verified account, in order to keep my deals live on craigslist without getting ghosted by them, but that's a much deeper discussion).It is incredibly easy to find lease option buyers.

I presume they are hard money lenders, since when I asked they verified that I would only have to pay the interest monthly, and then the bulk in the end.

I've used it to verify old landlords of applicants for rentals.

Did you have a contractor verify your rehab estimate?