If you haven’t already looked for these rules, you should check them out. Ebay doesn’t give you much information about shipping. They instruct to buy postage through them, but not what you can ship. They will give you a warning about media mail. Which is that you can’t send promotional items through media mail.
But a lot of people don’t realize what substances they can’t send through the mail. Some things need to be disclosed so that they aren’t sent up in an airplane. Alcohol is one thing that needs special care. Sure nobody is selling liquor on eBay. But perfume has a lot of alcohol in it. You need to disclose that and see how you can ship it.
It’s pretty interesting to read through some of these requirements. Laws about dry ice and live animals. Hopefully you aren’t selling anything that needs them. So some of what you read won’t really apply to you.
What doesn’t apply is how the postal service decides what they mean by height and width. This page goes into detail about the taping of boxes and what type of boxes you need to have. They give a detailed list of what is acceptable for a container to be sent through the mail. Did you know you can’t send odd shaped items through paper envelopes? You need to use a padded envelope for those items.
You can check out all of these rules yourself by using this USPS shipping rules Link. You’ll be amazed at some of the restricted items that still get sent through the mail. You might not have thought they were restricted but they are. Sometimes you might have to choose to ship with UPS to get your goods to the buyer. Of course many people think they won’t get caught. Well the postal service is a federal company. I’m sure the punishment isn’t a good one especially if somebody gets hurt because of your package.