Of course, but accounting for costs to exactly outweigh sales is a great way to get audited at higher income levels. Even if everything I account for is above board (which it would be) the cost of the accountant and/or lawyer to deal with the audit will exceed $600.It's true for every selling site so if you want to sell, you'll have to report on your taxes for every site you sell on if you go over $600 on that site. You can deduct your costs when you file your taxes so it doesn't mean you'll have to pay any extra tax.
My current strategy is simply to sell below the $600 limit (although Poshmark counts canceled orders to that limit, so may have already exceeded it) and then switch to a different platform (e.g. Mercari).
Of course, I don't sell Chanel bags. I'm talking Coach or Kate Spade.