Hi Ian,
Anytime you see a "for rent" or a "lease option" sign, ad, etc, there's a good chance that it is an investor either trying to rent or cash out on a property that they've fixed. You would simply gather some numbers, call them, and say that you saw their sign, ad, etc, and were wondering if they were interested in picking up anymore properties in that area. If so, explain a bit about what you do, and get their info. You would want to know their name, number, email, what areas they buy in, what areas they avoid, price range, type of property, amount of rehab they want to do, how many properties they plan to buy in the next 12 months, their prefered exit strategy, and how they plan to pay for the properties (cash, hard money, financing, etc). Sorry if that was kind of rambling, but just make yourself a form with that info on the computer and you will have yourself an action-packed buyer lead sheet :) Hope that helps. Anymore questions, post away.