https://store.usps.com/store/results/shipping-supplies/priority-mail/_/N-7d0v8vZ1dqlux5

Best boxes to use are the free ones, am I right?

When shipping Priority mail packages for ebay, Mercari and Poshmark, I try my best to use USPS Boxes. Click on the link, make an account and order your boxes. I reorder often before running out. Shipping times can vary, depending on the time of the year, so plan ahead. Here is a list of the ones I keep in stock.

https://store.usps.com/store/product/shipping-supplies/priority-mail-shoe-box—oshoebox-P_0_SHOEBOX

https://store.usps.com/store/product/shipping-supplies/priority-mail-box—1096l-P_O_1096L

https://store.usps.com/store/product/shipping-supplies/priority-mail-box—1097-P_O_1097

https://store.usps.com/store/product/shipping-supplies/priority-mail-box—1092-P_O_1092

https://store.usps.com/store/product/shipping-supplies/priority-mail-box—7-P_O_BOX7

https://store.usps.com/store/product/shipping-supplies/priority-mail-box—4-P_O_BOX4

https://store.usps.com/store/product/shipping-supplies/priority-mail-box—1095-P_O_1095