I have never heard of AT&T sending salespeople door-to-door.
It depends on the precise interpretation of "sending salespeople".
I have had AT&T send salespeople to my door (I confirmed it with AT&T) but they were not actually AT&T employees.
I'm still sore about it. <RANT ALERT>They told me a pack of lies (the first one being that they were AT&T employees) to get me to sign up for UVerse service. Then when the serviceman came to actually do the install, he told us the truth--but before leaving, he did a partial install and left the wiring in a state that caused it to fail awhile later. Then AT&T left us without phone/internet/monitored alarm for 4 days because they were too busy to come out and fix the problem they created.<END RANT>
High-pressure sales persons are taught that people are reticent to be rude and are also taught use people's politeness against them.
Learning to deal effectively with people who won't take no for an answer is good practice for dealing with confrontational criminals who often use similar tactics to close with a victim.