They have a vested interest in maintaining/expanding their business so just like card grading companies, they understand it's ideal for them to "create value" out of nowhere and if an auction sets a new record, it's not like they have to worry about due diligence to see if the price made sense or who the seller and buyer are and if they have a preexisting relationship or what, they just take their cut and that's it.
There are standard versions of these cards, full arts, rainbow-colored secret rares, and shiny versions, all of which have their own set value
But then you just have to look at the Alpha cycle of 1 mana coloured Instants: Healing Salve, Dark Ritual, Ancestral Recall, Lightning Bolt and Giant Growth
Graded Population Report: Charizard [1999-2000] #4 Visualize the distrbution of grades in the chart
With both cards on the battlefield, you can draw as many cards as you want and deal that much damage