Here is what I do in cases like this:
1) I treat everyone with respect, but I trust no one if I do not have experience with them or access to information that lets me verify who I am dealing with. I don't want to offend someone that may be a buyer, but I also do not want to be taken advantage of.
2) Ask them questions like were they are located. Check the headers of their email and find the IP address they are using. Most won't try to fake this using proxies and you can see if they really are in Kansas or Kansai. If they lie about anything, you have less reason to trust them, but sometimes people lie because they want you to think better of them, and not to rip you off. You can give them slack without trusting them.
3) You did some research, which is EXACTLY the right thing to do so you can find out more about this person. Search Google for their email, name, address, and other domains they own if you can. Ask what forums they visit and other things to learn more about them.
4) If you want to sell to them but do not trust them, then either use an Escrow service, a third party you trust, or just ask for payment in advance. And make sure you have the money in your account or your hand before turning over the domain to them.
5)They may argue that they do not know they can trust you either, but you can fight that arguement by telling them you are a trader here. While you don't have much itrader reputation built up yet, it should help. You can offer to add their first name to the admin contact of the domain to prove that you own it and that you do intend to sell it to them. Do NOT put any of their other information on the domain until you have been paid.
6) If you are really uncertain about them, tell them that you will need to contact the payment service like PayPal to verify that they payment is being made by the person that owns the account. That is, that the payment is not being made with a hacked account. And the payment email address must be something that you can see belongs to the same person you are dealing with.
Honest buyers will understand you having rules about selling. Most crooks with stop talking to you quickly since even if they want to try and rip you off it will be much more work than they are used to. And if you do have someone that goes away, please post about them to let others know. You don't have to say they are a crook, just that you didn't trust them and they stopped contacting you.
Good Luck!
