A bug extermination person came to my front door bimonthly spraying around the house for one year and kept offering to drop the price each time I said no. I ended up buying one day of service only. Then I went to Yelp and Google and saw the complaints about this company.
How much clearer than "I can't afford this" do you have to be?
I'd get sales people knocking on the door for some sort of energy company. It's not worth their time as I don't use much electricity except for air conditioning season. They are an annoyance.
But it happened often enough that a "no soliciting" sign was put on the door.
Would you believe there are still people who knock on the door and tell me they aren't selling anything. It's still always some energy company, usually someone around 20, trying to flip you to their service.
They don't understand the premise of no soliciting so I teach them what it means.