Fred, yes, I am a CPA, but my certificate has not been active/current since I retired in 2007. I probably am a rare CPA in that I have never done income tax returns for anyone (or any company) other than myself and my family members. FYI, the two major chunks of my career (16+ years each) were spent with the USA subsidiary of a British company where I was mostly involved in contract administration and with the finance department a large county government (which doesn't pay income taxes). However, I do know enough about income taxes "to be dangerous."
With respect to the cards I've sold that I got out of wax packs as a kid, while my cost of these cards was zero, I did have some costs to offset against what the cards sold for, such as TPG grading fees and eBay selling fees. The profit on collectibles sales (total sales $$ minus total costs $$) becomes part of one's federal taxable income, and this amount could be enough to put one in a higher
incremental federal tax bracket. Here's a link to the federal tax brackets for 2023:
https://www.irs.gov/filing/federal-i...other%20filers
You asked, "how does state tax work on that?" I believe state income taxation varies considerably. Having lived in VA my entire life, I am not familiar with other states. In VA, one pays the same income tax rate on the profit on collectibles sales as one does on other types of income.
Fred, I hope I have adequately responded to your questions, except for those you raised related to selling cards as a dealer, which I don't feel I have enough expertise to answer.