if someone does not want and unwilling to show the receipt on Ebay and willing to disclose serial number. Still not an honest seller ? One safeguard is get the serial number and will clear all the doubts.There is no way you could find out if its stolen item or not maybe later on cops show up. Honest ebay sellers always posted a receipt. If i were seller, i would post receipt and grab a pic of apple store online checkout with specs. I would not give out serial# if i were you.
We can debate this issue till the cows come home, I had bad experience with a seller who sold me a mbp, got the serial # and end up different serial # on the item, what a day light robbery that was.