But what about multiple items
I haven't done it yet, but I've seen many sell multiple items instead of one item per post. As a result, some of the items are sold and some aren't. So the post itself can't be moved - I agree to NOT deleting the post as some history would be good. I see that on most the sites selling used Ham Radio gear; please keep the History.
Problem is, most the sites that do cause grief in viewing "for sale" are those multiple items sites. I have to go through them again and again - having my heart broken each time as I'm reminded of the "deal" I didn't catch in time - in order to see what is left.
I have seen the seller update/edit to Sold (or not) on each item in his initial post and sometimes summerize the current state of sold/unsold in a later post - that is helpful if there are a lot of items.
I think I also saw one seller replace the sale price with "Sold". Though letting us know it was sold, that does remove the history for future sales.
If the moderator is going to Move an item Sold, I'd think it is just as easy to mark it sold in the Subject line. And if the seller has multiple items for sale, it would be kind to update the intial post marking each item as it is sold - but keeping the Sale Price in the post.
My poor unwanted really really warm parka has so many "reduced price" stickers, it might be difficult to see what it finally sells for. But as it is only one item, it will be easy to just a mark the original post Sold.