If the tool was advertised as "Used: An item that has been used previously. The item may have some signs of cosmetic wear, but is fully operational and functions as intended. This item may be a floor model or store return that has been used. See the seller’s listing for full details and description of any imperfections.", and he didn't mention anything about the markings, but took numerous pictures of other angles not revealing the markings, I'd consider it shoddy and not in good taste. However, I don't believe he was necessarily obligated to mention the markings...it would make me mad, though, and that's why I specifically ask about markings before bidding on any "Used" tools.
However, what gets me is sellers who advertise an item as "New: A brand-new, unused, unopened, undamaged item in its original packaging (where packaging is applicable). Packaging should be the same as what is found in a retail store, unless the item is handmade or was packaged by the manufacturer in non-retail packaging, such as an unprinted box or plastic bag. See the seller's listing for full details", yet the part clearly shows some wear (even if only handling wear), or the item is clearly not in the original packaging. It amazes me how many sellers are capable of listing items without knowing how to read.