Wanted to follow up with a resolution. After my initial annoyance I reached out to the buyer and asked if I could help them with anything. They said that they expected a brand new item to have all the parts. I politely apologized that they were unhappy with the order, but pointed out that the item is listed as used and the description noted that the item did not come with that accessory. I offered them the opportunity to return the item at my expense. The buyer messaged back that they reviewed the listing again, would like to keep the item, and asked if there was a way for them to revise the feedback. They did that and changed the review to a positive, so it worked out really well.
In regards to the listing format, I only put incomplete on an item title if the item is missing a part (an action figure is missing an arm, a transformer is missing a wing). The only exception to this is if the item is in its original box and its missing its accessories then Ill note that in the item title. In regards to the item condition, I put a detailed description of what is included in the lot. I feel that this section is where any clarification to the broad term of USED needs to be placed. I don't rely solely on the picture to reflect whats included as whenever I see another seller do that it raises red flags. I have never had a problem with this and this is the first time I've ever had someone complain that an item was not included when the information reflected it did not. In the past, if I made a mistake with the listing, or if looking back I can see that it was ambiguous, Ill take the blame for it and either offer a return, a discount, or in some situations a full refund and allow them to keep the item.
I appreciate everyones responses, Im glad it ended up working out.
