Of course there are always exceptions. The polite thing to do is respond to the person asking them to be a bit more specific. I have found a good ruling guide is, if the person includes nothing of their info in their letter to you, disregard the message completely. I find it very odd when people inquire about my personal family tree, yet guard against revealing their first name to me. Also, when presenting information to others do not forget to consider what others may wish to keep removed from public record.
Some people are sensitive about their true age being known, for instance.
So you have to exchange your data wisely. To sum things up, simply use your common sense and be courteous. Most individuals who explore genealogy are friendly and thoughtful. They love the thought of family and are looking to gather more into their fold. And remember, even though you might not find a connection with someone, you may find a friend.