Here's a package I got in the mail today, with the coin it contained on top of it. You can see the disparity in size. I can't stand waste and it really bugs me when people use these huge envelopes to send little items. I know some of you will say it's better to have it too protected than not enough, and of course that's true, but there are little, much more appropriate sized envelopes available. This is a big waste. They could have mailed a dictionary in this envelope.
Ive had that happen to me, big yellow envelope for a tiny roman coin. Sometimes its double packed with a smaller yellow envelope within the large. Silly.
It's also possible that it was the only appropriate packaging they had on hand. It's big enough to re-use, so keep it for your next sale.
Bigger package is less likely to be tucked into a pocket... It may also have been cheaper to buy one size envelope based on what s/he usually sells.
I think your instance was silly. I do believe that bigger envelopes stand a better chance of not falling into cracks and getting lost though.
99% of the time the packaging I use (when it isn't USPS Priority provided free) is reused from a previous shipment. I get envelopes like that used as inner packing to protect an item and they all get saved! I'm not saying that was what was done here, I'm just saying if you bought from me there are good odds you may get an overkill packaging job from time to time, but it's ALWAYS reused. My 2 cents.
That's another thing. This person made no money on this sale. It was a silver Canadian 50 cent coin buy it now for $2.50 with free shipping. I would have expected it to be shipped in a regular envelope with a stamp.
Try buying a micro-SD card from Amazon. You could fit an entire camera inside the boxes they use to send those.
You just can't please some people. If it's not "too much packaging" it's "not enough packaging". The coin made it to you, that's what matters. Recycle the envelope. Move on.