That post got me thinking too. I often charge $3 or $4 for one chip! Maybe a mistake, maybe I am wrong, but I include for these costs -- costs I wouldn't have to pay if I were a dealer with a table selling for cash. I set my price as though I were selling arms length, so use shipping charge to pay for:
¶ eBay and PayPal fees. PayPal fees alone are something like $1.02 on a $25 receipt.
¶ ink, cost of printer and paper and envelopes for PayPal shipping labels.
¶ handling, wrapping.

Robert