You rarely have a PROFIT from a yard sale. If you sell something at a PROFIT (sell it for more than you paid for it) then the profit is a capital gain and you are supposed to pay tax on it. If you sell your old $500 couch for $50, trust me, the IRS does not want to know about it and you can't deduct the loss.
If you sell a couch you bought for $50 for $500, they DO want to know about that. But it's not business income (unless you have a used furniture store), it's a capital gain. It all has to do with profits.
Don't know where the chemistry tutoring comes in but you can be sure that will be taxed in some way.
Not knowing where MissyH lives I can't speak about what her state wants, but I went over all this with my tax preparer two years ago when I was selling junk on eBay just to clear out my closets, NOT as a business, and that's when I learned the difference between capital gains and profits from selling, say, Avon products where you are doing it to make money and have a business. (We also went over hobby stuff.) My state doesn't tax anything the IRS doesn't tax.
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I pray it does not occur that the last thing I did before I died was vacuum the house or eat broccoli.