How to do a trade-in via eBay?

[brecs]

Background: I've been an individual buyer of items on eBay for my own use for many years; I've never been a seller.

A couple of months ago on eBay I bought a used item in the Business & Industrial category from a seller who has long been in the business of selling and servicing used items in a specific sub-category and who sells exclusively on eBay. Items are typically priced in 3- or 4-digit dollar amounts.

The transaction a couple of months ago was perfect and I have used the item without problem. However, the item -- as I knew when I bought it -- is a model discontinued by the manufacturer. The seller is now listing a later model than the one I bought, at a significantly higher price. I would like to trade up to this newer model.

Both the item I bought, and the one currently listed by the seller, consist of a used base unit plus several new/unused accessories. It is the base unit that I want to upgrade to the newer model; the accessories are identical. The value of the accessories is a significant proportion of the total item value, and they occupy a majority of the shipping volume.

I could buy the newer one -- including the unneeded accessories -- and then list my older one -- including those accessories -- for sale. It would be much more efficient in several respects if I could just send my base unit to the seller as part of the purchase price of the base unit in the listing, with the seller just keeping the accessories. (The accessories could be included in the seller's presumed future listing of my traded-in base unit.) I want to do this in a way that would not violate eBay's policies. I think that means, at a minimum, that the value of the trade-in be included in the total transaction price as seen by eBay.

Is there a way to do this base-unit trade in? You may assume that I trust the seller and don't expect them to trust me; e.g., I'm willing to ship them the base unit I have before they ship the listed one to me.

Thanks for any ideas or info...

[dryophelia]

@brecs 

Trade ins don’t work with the eBay model.

If you buy this current item, you could sell the unwanted parts from the original sale. 
My spidey senses would be tingling if a buyer requested what you have proposed here. 

[brecs]

@dryophelia , thanks for the response. Assuming you're right -- and I've no reason to doubt that you are -- my intense dislike of inefficiencies is highly irritated.

[femmefan1946]

Contact the seller and ask if they are interested.

This would have to be an off-eBay transaction, but it sounds as if they are an  established business.

In this case eBay was the matchmaker who introduced you. The rest of the relationship is up to you.

[mtgraves7984]

I'd suggest that you go back to your seller and see if they allow trade-ins and if they can work with you. To be honest... I doubt you'll find anyone here that isn't selling, straight-up. Good luck.

[soh.maryl]

Odd to see an experienced eBayer seemingly recommending an off-eBay transaction.

[james37433]

If there are people that you have dealt with in the past, is it within the rules for me to sell mine and buy yours.  Note that I am not trying to cheat ebay, so for fees purpose, we use a fair value for each and appropriate shipping charges.  In the end, ebay gets the usual fees for the two items and each of us gets a trade with the fees and postage cost.  This is not a trade where each of us sells valuable items for 1.00 and therefore shorts ebay a large fee x 2.  In the past, people sold things for 1.00 plus a 45.00 shipping fee because ebay only collected fees on sales, not shipping.  That went away quickly when they collect fees on all.  If each sold the item to someone else, that is acceptable.  What is less acceptable about each of us selling it to each other?  Same fees and shipping