Sellers can source inventory from various places, and then sell it to a large and enthusiastic audience
It that creature attacks, it untaps, and a second combat phase begins after the first
That's actually a rather impressive design step, and as much as we bitch about how each individual color's cards for interacting with the other colors suck, and how the cards designed to let them interact don't really play to each other's strengths, this is still huge
We have a lot of cards with this treatment, including 10 uncommons, 26 rares, and 14 mythics
Products like Commander decks, Modern Horizons , and Masters sets quickly became extremely popular and continue to this day
Card grading services are professional at it, and while how much it costs to get your card graded is a big discussion, for 100 of the most expensive cards that are worth hundreds or thousands of dollars, it makes sense and builds confidence and trust in your buyer