Or instead of lying like a child you could just say "No" and close the door. It's not difficult.
Not only will you save time but the person at the door can get on with their job and talk to more people.
Oh and a fun fact, those signs mean very little if you don't have the balls to just say no and close the door, as a fund raiser in one area I got 3 sign ups in 2 days from people with a "NO COLD CALLERS" sign.
OP: There is so "season", however charities move around areas regularly so it's possible your area has just been left alone for a while.
You obviously don't have two young kids then
Or a doorbell - or door that wakes the whole house up when banged on.
Because the last guy that rang my doorbell trying to sell me Sky ( even though I had already spoken to him 6 years in a row ) whilst I was trying to feed my 10 month old - and stop my other kid from running towards the front door - got an absolute earfull - and I actually think he could see why.
Not everything is black and white - and if I wanted stuff, whether it is Sky, Salvation Army contributions, oven cleaner, perfumes, phone contracts or any other rubbish - I will research it in my own free time - and not the time that suits a seller. So YES - they can damn well naff off....
90% of people know what is available to them these days - they don't need someone knocking on their door trying to use trained techniques to sell a product. I actually had a guy from a well-known Broadband provider try and give me some small talk about how good/nice my car was......It wasn't until I asked him what he actually knew about the car in question ( and not what he had been told to say in his training class - that it all went pear-shaped for him ) What was funny was - there were actually two of them knocking - one with a clipboard, the other for backup. It was like a scripted double act....