Hello @Emma111! Welcome to the community!
You are correct about the sales tax requirement being new. Recent changes in sales tax laws in some states require OfferUp (and other online marketplaces) to collect and remit sales tax on certain sales.
For shipped items
We determine the sales tax rate based on the ship-to address of the buyer. If your ship-to address is in one of the states below, we will collect and remit sales tax on your shipped purchase.
For items picked up in person
The sales tax for an in-person transaction is based on the location where the item was posted. You should note that OfferUp does not collect taxes on sales that are paid in cash or through an off-platform payment service, so if sales or use taxes are due on such sales, you will need to manage that yourself.
This is just a brief summary of the changes, but we do have a Help Center article that goes over this in more detail.
I hope this helps - let me know if you have any questions!