This, so very much this. I love what Jeff Thull says about this... "always be leaving" (as opposed to "always be closing"). Make it clear to the prospect that you are not going to be the stereotypical sales-person who grabs onto them like a little pit-bull grabbing onto your leg, and who won't let go until they've been beaten over the head with a stick. Show them that you respect them, and leave as soon as it's clear that there isn't a good fit. Leave a good impression and later, when they do need your "thing" they're more likely to call you up (or take your call when you call again in a year).