Been I personally never make encouraging noises if I'm not feeling it. But when I first started out, I definitely had a few akward moments where the other party were very keen to exchange numbers and the 'lets do something again sometime!' chat, and then when I would message them I would get the 'Oh, actually I'm not really interested' response. So I suppose thats also what has driven me towards no message if I'm not interested.
change I suppose everyone is different and it really depends on how the dates went I suppose. I think many people would rather take the easier option of not messaging rather than have the awkward conversation - especially if there is a chance that the other party is more keen and might take it badly. And again, for me it really comes back to how invested you were. I was upset when someone I'd been friends with for a few months and then dating for a few months broke up with me via vague text and no real explanation. But if someone I've only been on 2-3 dates with and was a bit meh about didnt respond or slow faded out of a conversation? I'm honestly not going to be too fussed about that. I might wonder why, but that would probably be it. But then I've also perfected the art of under-investing, so...