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Rates are those used by the post office using size and weight of the package and shipping zip code versus destination zip code. Ebay has a video about shipping here: https://www.youtube.com/watch?v=mxmpR1d5JbM
I would suggest you package and weigh one item and go through the motions of listing it. You don't have to actually do it, you're just practicing. It's much easier to understand once you actually do it. You are still allowed to charge a fixed amount for shipping, but customers do tend to be wary. People who buy on Ebay are aware of what something should cost to ship and don't like it when shipping charges seem excessive.
You can check out www.usps.com It will show you exactly what it costs using various types of containers (flat rate box or envelope, your own box, etc.) as well as types of shipping (priority, book rate, etc.). Ebay uses the exact same site.
I don't think any customer objects to minimal charges for things like bubble wrap or buying a box. It's the outrageous prices they object to. No one wants to buy a $5 item and be charged $10 for shipping. I've never had a problem with anyone complaining and I've occasionally sold items on Ebay for at least the past 8-9 years.