lower of cost or market works. if you sell items purchased at a loss they're deductible if you sell personal items at a loss, those losses are personal and not deductible. if you sell personal items at a profit, those sales are taxable. another thing you should be aware of. if the activity produces net losses in 3 out of 5 consecutive years
the IRS could classify the activity as a hobby. as a hobby certain expenses would not be deductible.
read the following thread
https://www.investopedia.com/terms/h/hobbyloss.asp#:~:text=The%20hobby%20loss%20rule%20of%20the%20In...
