Card shops and distributors would gets these, usually a couple months in advance of the release. Sometime card companies sent 1 card, sometimes 2 or 3, and in other cases, 10 or more. It varied from company to company and from product to product.
Then, some of the recipients would have regular customers of certain players (or teams), and when those customers would come in or contact them, they would include them in other sales to the customers (or give them directly - or sell them - there was nothing on or about them stating that they couldn't be sold.)
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).