Most Helpful Guy
Politely refuse. The example reply you gave in your update is great, just instead of saying 'Sorry, but I am looking for something else' just say 'Sorry, but I'm not interested.' Guys might message back saying you don't know them enough yet and that they might have what you're looking for if you accept them and it can lead to a lot of pestering. It's not a good idea to ignore someone's messages at all. It leaves off on a much more negative feeling on average compared to politely refusing and it can make you look rude or cocky if you don't reply because it makes it seem like they aren't even worth a reply which is just a part of human decency.
There will be guys that get upset about you no matter how well you put it. It's just how some people are. They take certain gestures as an attack, feel undervalued and/or feel the need to lash back or prove you wrong.
Don't take any of these things to heart or feel guilty about it. The important thing is that you made your intentions clear right from the start and tied a loose end at the same time.
Most Helpful Girl
I'd say don't reply. I never double message, no reply to me means not interested and others should realize that. How would it sound if an interviewer called you and said, Hello, is this Miss Tortoise?, oh yes we're calling to let you know you don't match the skill criteria and we will be giving the job to someone we find competent, okay bye now.