I never lost a customer who wasn't moving. I did lose a couple of elderly folks who died, but always managed to get the new homeowner to sign with us. I kept my customers with first rate personal service, charging a fair price, and not making them sign long-term agreements that were in my best interest instead of theirs. I sell what folks need, explain how it works, and why the "free" or "discounted" stuff isn't so attractive. I promised upfront to keep their business with outstanding design, user-friendly and effective, reliable systems, and VERY fast response to system problems. I kept my end of the bargain, and they kept theirs.
Of course, my customer base was upper-middle and upper income folks, so the ADT's and other resi "pushers" weren't much more than extra confetti in my customer's shredders. There are very few ADT signs in exclusive neighborhoods.
For the record, if any of my customers was/is (I sell wholesale CCTV equipment to installation companies now) of the mindset that they would seriously consider a "giveaway" system, I would not want that customer. That type will cause collection headaches and is only loyal to whatever this month's special is, value and service be damned.