wrote
.........................

Note, I'm not saying that this guy proposing to sell you all the
shingles you need, while only listing one box on Ebay is not a
.........................
violation. I agree that with his giving you a sales agreement for
the transaction outside of Ebay it is a violation of Ebay rules.
But I'd like to see where it says that if you do a legitimate
transaction on Ebay, but learn the buyer wants some additional item,
like the nail example, that you then have to put the nails through
Ebay.
...........................

Until someone shows me where it says otherwise, I say the answer is
NO.
=====
C'mon...aren't you going to ask the friendly folks at
alt.marketing.online.ebay?
They love these profoundly complicated questions of great national
importance.
I'll bring the popcorn.