Possible hidden costs?

When an item is sold is the money you recieve it.  Are there no hidden costs. Or is there any future costs a seller has to keep aside for the sold item? 

If you have a store, use subtitles, or promote your items in any way, you will get a separate invoice for those fees.

No store just a regular person

If i dont do any of the 3 above does that mean i dont have to worry about any future fees?

Not exactly a hidden cost, but be aware that in the event of a dispute, you may be required to refund the buyer.