I have had Amazon ship me at least what appeared to be previously sold and returned lenses if not used ones.
Missing warranty cards, disorganized packaging that does not appear from the factory, signs of box been previously opened, etc. Not that I mind being shipped a lens that was previously opened and looked at as long as everything is intact and works factory fresh. But missing items and/or misses expectations/not what I wanted, it goes back. Also, Amazon has been spot on with arranging a replacement which is why they are the first place I shop. They do differentiate between defective/error based returns wherein they pay the shipping both ways vs did-not-like/want kinda returns where the customer pays return shipping and at times the original shipping as well.
10% markups are from other galaxy??? Yeah right! A lens that sold for $2198 sells in the range of $2498 to $2798 after the unfortunate disaster in Japan without a formal price change from the manufacturer. Same for camera bodies! And then when the instant rebates come through, the prices go up by 70% to 100% of the rebate amount! So yes, the markups are definitely there...doesn't matter how it's split, that's a different story and is irrelevant from a consumer standpoint.
Lastly, one of the foundational aspects of e-sales is to provision for (trial) purchases allowing for a return if the item is not liked by the customer. If I can't see it before I buy it, then I would want an option to return it.
I don't find any ethical issues with what OP posted as long as the interest/intent is genuine. That said, I would definitely call it unethical if one was to do this only to save money on a lens rental.