You have no idea how sketchy these companies are.

ZoomInfo (public company) for example provides a free plugin for sales people which is scanning email for all the email signatures and then they sell all that data to their customers. Even crazier is they take data from their customer’s CRM systems.

DiscoverOrg is buying data from third parties without really knowing how they got the data.

There are a bunch of apps and browser plugins that read your emails or contacts and then those companies sell that data to third parties like these data brokers. I use very few browser plugins because of this threat.

If you have somehow acquired a list of contacts you can get a lot of these companies to purchase it with very few questions.