NEVER ship until payment is final. That would have save you some time
and money. At least you have the item back. Too many sellers have this
happen and they're out both money and the item.
The package indicates Commercial Base Price, which is a discounted price
high volume sellers get. So, they probably make some small change on
shipping.
Try looking up this set on addall.com, abebooks.com or one of the other
umbrella sites featuring hundreds of sellers. They're easy to use and
give you a range of prices for similar books.
Have a little patience. It is a holiday weekend and Monday has not come
to a close yet. If you still haven't heard from the buyer by Wednesday,
I'd email again and say you'll be opening an unpaid case if he doesn't
pay within the next 24 hours.
Definitely notify the seller first, before you do anything. That's the
fair and correct action to take. I often sell vinyl records. The only
"new" ones are those still in shrink wrap. We test play all other
records and those that we deem perfect, we ...