Would you take a worn bicycle and a used lawn mower in exchange for the brand new bicycle you received as a gift (or won in a lottery)
If a lawnmower or whatever additional item/s I received in the trade were more useful to me than the brand new bicycle collecting dust in storage, I sure would make the trade.
when you have a bike you're comfortable with and have customized to your liking (and thus don't have a use for the new one) and live in an apartment?
As I said earlier, "If a person had a use for the knife it wouldn't even show up on the trading window." This means that the individual you are trading in the wilderness or all the people in a village or lone dwelling already have enough knives of whatever quality they are happy with.
The additional items, along with the lesser quality item, are something that the person with the higher quality item has a use for. The person could keep the higher quality item collecting dust, or they could have a lower quality item collecting dust with the addition of other useful items that were included in the trade.
Also, the lower quality item is more likely to sell since more people can afford it.