If you’re ever shopping in like a poster tube, put the barcode top to bottom. Can’t scan around corners. More on reddit.com

With the USPS, you've got two main options: They have flat-rate boxes that cost a set amount to ship no matter what you put in them. If your stuff fits, that's an easy way to do it. They give those boxes to you at the post office. You can also have them mailed to you ahead of time, but if you wanna just get the thing in the mail, simply going to the post office and doing it is fastest. Pack it in whatever box you want (smaller is better for shipping cost), and bring it packed to the USPS and tell them you'd like to ship it. Reused boxes are fine. If the box has labels, X them out or rip them off... or at least write over the barcodes so it can't be accidentally scanned somehow. They'll hand-hold you through the process, but it's really just filling out the address label and deciding what kind of shipping you want (if you just wanna get it there in a reasonable amount of time without spending a buttload, ask for priority mail). The other services work about the same way. If you're gonna pack it at the post office, save some $$$ and bring a newspaper or just some printer paper to crumple up as packing material. It's biodegradable and they'll charge you a pretty penny if you want to buy packing material at the post office. If I have the foresight, I grab a flat-rate box from them ahead of time, pack it and address it at home, and bring the box ready-to-go to the post office. More on reddit.com

I mean.... isn't it all here.... https://faq.usps.com/s/article/Can-I-Ship-Lithium-Batteries https://www.usps.com/ship/shipping-restrictions.htm More on reddit.com

This is vital advice. I get so tired of dealing with sellers who don't even try to ship things decently it's exhausting. Another tip to add is don't use rubbish to ship stuff in. Reuesing a shipping box is perfectly fine but I received probably ten items in cereal boxes, soda cartons etcetera and those WILL NOT hold up to being shipped. There is a reason those items show up at grocery stores in another box and it's because they're flimsy. More on reddit.com