Chris & JY,
It would be a great idea to have as large a buyers list as possible. Eventuially you would have a handful of buyers who use you as their eyes and ears for finding good deals. I would suggest going in there as if you are the buyer, with a partner that will have to approve the deal. That way you always have this other party you have to have the deal subject to his approval. Your not lying because the partner is your buyer. Here at BiggerPockets, there is a link to Forms and Publications. One of those forms is a Bird Dog Agreement. It's a PDF so you will have to re-type it for your use.
http://www.biggerpockets.com/forms/bird-dog-agreement.pdf
Using this form, you have a good understanding as to what the buyer owes you if you find a deal for him. Of course, he can still try to go around you, but probably wouldn't for reasoins previously mentioned.
FMV should be a combination of several sources, including:
1. A realtor's opinion
2. Your own analysis from going to open houses, and seeing what homes in the area sold for that are comparable.
3. The websites such as zillow, cyberhomes, trulia, Eppraisal, rentometer, zilpy (for rentals), and the tax assessor's site. Realtor.com also has some sold information, or your realtor can run a sold search report for you.
4. An appraisal (probably not due to the cost)
Your purchase and seal agreement should have some "outs" especially if you are not sure if the house will sell easily. An inspection clause with as long a time period as possible, is one way.
Of course in a perfect world you would have your buyer all lined up. Good luck, Mike