I've purchased several pieces of furniture from auction where the original owner has placed more than one cash upgrade on the piece. In one case someone purchased every credit upgrade for their hanging decoration possible (265 credits total). Why are people allowed to create this type of franken-furniture? It is expensive, of limited use and difficult to sell at auction.
Why not lock furniture to a single credit upgrade? Or, to get a bit more complicated how about a system to transfer upgrades between objects. Maybe something simple where you can drag an upgrade from one piece to another. There would be no net loss or gain of credits or furniture just a redistribution of upgrades already purchased.