I could see the writing on the wall. Offerup I think does this. If you click through an item in a search the URL has a UID in it. Then if you click on the se

I could see the writing on the wall. Offerup I think does this. If you click through an item in a search the URL has a UID in it. Then if you click on the seller and find the item from there, its an integer (which is likely a database index).