You can set up your own shop, and then set the items that you want to sell as 'For Sale' - I did that with my photography studio. I'm not sure if it keeps going if you sell the shop, I would assume so, because if something is labelled as for sale then there is an option to restock. I dont think you'd be able to sell your items to it though once it was owned by someone else.
There is a SimBay mod by LittleMsSam that I use for my archeology finds, that does the same sort of thing, and makes the selling items thing seem more realistic. You go into the Sell Via Simbay option on the computer and the item sells and you can only sell 4 things a day.
https://littlemssam.tumblr.com/post/175412741998/sell-via-simbay-simbay-is-our-new-unique-selling
I don't think you can sell vegetables or fish though.
