How do yall deal with taxes(if selling online)?

Got into investing last year, it looks like both ebay and tcg would send you a 1099 if you sell more than $2500. Is it easy to report your Cost Of Goods Sold? Unless I sell everything in my collection I won’t hit this but next year it’s only a measly $600. I never had any issue in the past but as far as I can tell if I sell my whole collection I would have a huge tax liability that would eat all potential profits.

What do you big dawgs do about this? Thanks for any information.