They typically offer 60-70% of a cards market value in cash, but often provide a kicker for taking store credit, bringing the value up to 80% or more
You probably will be generating a lot of money if you have specific cards or first-edition cards (apart from Machamp)
So, to make this work, run Reliquary Tower and other ways to keep from discarding, on the sly, and then run things like cheap spells and permanents to keep you up in your colors
This is just another kindred deck
There are others who are die-hard Alpha collectors and have dedicated many hours of their life towards detecting fake Alpha cards from a field of real ones
Mechanically, it is more or less a rework of Rapunzel - Gifted with Healing from The First Chapter, carrying almost the exact same effect, but as an action card, and being potentially slightly less flexible in real play