Skilled, experienced deck-builders have some developed statistical intuition and, of course, do not need to calculate such statistics all the time
Unlike the Thick Grey stamp which may have formed by stacking printing sheets before they were properly dried, I think Thin Grey stamps are indeed due to being low on black ink
Ojer Axonil, Deepest Might / Temple of Power Listed at: $12 Ojer Axonil, Deepest Might thrives in red decks that feature instant and sorcery spells
You can also use it in your inkwell, but unless the situation is dire drawing cards is almost always going to be the better choice
Im not going to parse out the best or worst ones here, but they all kind of fit the description
There are stock alert pings, people sharing successful finds in the wild, and links to lotteries (like the Amazon one) run by other independent shops