Re: They'd save a bloody fortune
"If they stopped sending me "sign up" junk mail every few days."
Last time I spoke to someone who knew the marketing business, he said it depends on the industry and saturation rate in an area. It's often cheaper to mail-bomb an area to every "Dear Occupier" than to target specific groups, eg non-customers.
I'd imagine we will see more of this now with GDPR in force as to produce a marketing list of non-customers, someone has to subtract the customer list from the full list and that's most likely to be the 3rd party marketing company. That means handing over a very valuable dataset along with the inherent risks of allowing all that personal information out of your direct control.