I'm very fortunately to have never been through anything like that.
I have never had a blind date.
I have connected with guys I had previous crushes on, only to find out I no longer had any infatuation or crush with them, so, I just told them that it was nice and maybe we'd run into each other again sometime.
I think there are subtle ways to let people know you are not interested, without being harsh or mean.
I also think guys picks up on queues. People are born pretty intuitive. They can tell if something is there or not.
The hard part is when you really enjoy the person as a person/friend only, but the other is crazy about you. Because you both want to stay connected, but for different reasons. The person less connected has the responsibility to make the sacrifice of letting the relationship go.