There is a marked and distinct difference between business expenses (such as rent, utilities, et al) and capital assets or inventory.
If the enterprise would otherwise be considered to be a business, then the cards would be merchandise and factored into the COGS calculation (and deducted). Even retailers selling marijuana (legal under state law but not under federal law) are allowed to deduct their COGS.
If the activity of collecting the cards does not rise to the level of a business, then the cards, themselves, are capital assets and their cost can be deducted from the selling price. If the cards were held strictly for personal use, then no loss could be recognized. However, if the cards were purchased and held for investment purposes, a capital loss would go into the netting process and could be recognized.
