Spammers won't usually address you or your ancestors by name. Spam is usually email sent with the purpose of selling something, getting you to click on some link or other, and is usually sent to multiple recipients at one time.
Most folks who will contact you thru WikiTree do so because they find your name as a profile manager, and they are genuinely interested in finding out more information about their ancestor. You'll probably notice that they aren't asking for any personal information from you, but rather might want more information about the relative they found you have in common. Sometimes they're so excited they don't make much sense... Remember when you were first starting out your genealogy search?!!
It's always good to be cautious about the information you give out, but just because you haven't met them yet, doesnt mean that you can't be related somehow. I broke through a MAJOR brickwall from a stranger-turned-relative contacting me with information she had found in her husband's great-aunt's attic!
Be friendly! Share information on deceased ancestors, and in turn they may have more to share with you. If you don't feel comfortable extending a WikiTree invitation to them so they can participate as well, please forward their email to us at info -at- wikitree.com.
Any other ideas?