With the cost of postage recently increasing, I have to ask myself if it's really worth it to sell on eBay. The shadowboxes I sold cost $4.60 to send in a postal Priority Mail (free to me) box, and $4.30 to send first class with me providing the box. Since finding the right sized box for thirty cents or less was impossible, the choice was easy. But, if someone is paying $5 for an item postage at that price doubles the cost. I'm sure that has made a lot of people think before bidding.
I've started to watch the size of the artwork I list for sale because mailing larger pieces can get quite expensive. In the future, I'm only going to sell artwork that will fit in flat envelopes or bubble mailers, no more boxes for me. I don't want a customer paying twice as much for postage as they paid for the artwork.