Let us know which side you take – would you respond with a “thanks but no thanks”?
If you want to acknowledge that they put the time into the e-mail, you can say, “Thanks so much for your thoughtful e-mail.
After reading your profile, I don’t think we’re a match, but best of luck to you!
Start with thanking him for coffee, lunch, whatever. Then tell him it’s not a match: “Thank you for treating for coffee and our interesting discussion. And it wouldn’t be fair to you to accept another date knowing that I don’t feel the spark I know needs to be there to develop a relationship.” He said he was disappointed, but he understood.
It is uncomfortable, but you need to be gentle yet honest — up to a point.
It is my experience that most people would much prefer to get a polite, “Thanks for your interest but I don’t think we’re a good match.