Soft Opt-in - Is it real?

I have been tasked with researching the "soft Opt-in". Maybe I haven't been paying enough attention, but I haven't notice the idea surface on any of the regular channels that I monitor for best practices and legal processes for Marketing email.

In short, this I believe sums up the concept of Soft Opt-ins...

• they have obtained the contact details in the course of a
  sale (or negotiations for a sale) of a product or service to
  that person;
• they are only marketing their own similar products or
  services; and
• they gave the person a simple opportunity to refuse or opt out of the marketing, both when first collecting the details and in every message after that.

Apologies if this is old news and dealt with long ago. I appreciate any feedback or redirection.