I am an accountant. This comment is for discussion only and not to be used as tax advice. Consult your tax advisor for your specific situation.

Ebay reports income if you sell over $20,000 [edit: earned in 1 calendar year], and then once you're on their 1099 list, you don't come off it even if you sell less. The actual IRS 1099 reporting threshold is just $600 per year. Ebay is appealing to the IRS to try to limit their reporting burden. They will eventually have to report all sellers that exceed $600, but they keep getting that pushed back.

FB also issues 1099s now for sellers. I am not sure what their made up threshold is, but Marketplace has asked me for my tax info. I just took my things down and told it that I hadn't sold them through Marketplace. And I just noticed what linearchaos suggested... list the item as 'ask for price'. That may cut down on potential customers though. I know I scroll past items that want me to ask for price.

Do not worry if you sell enough to be issued a 1099. As mentioned before, you can subtract the cost you paid for the items, all ebay and paypal fees, and even shipping costs if you don't charge separately for it, likely resulting in an overall loss. So no tax likely. Tax is only calculated on net income. If you start flipping obscure items of value from thrift stores, then you might get into taxable net income territory.

Finally, to your question on does it count against your unemployment benefits. Likely. However, Ebay/FB don't report their 1099 vendors until mid- to late- January 2025 for annual 2024 payments. The reporting deadline is Jan 31. So you don't have to worry about it until then, and again only if you exceed their made up thresholds for sales.