Relisting

[renefindlin-0]

I have an item that didn't sell. I got an email asking if I wanted to relist it.   I have relisted it a few times dropping the price each time.  This time I dropped it to the absolute minimum and changed the duration from 7 to 3 days and a $1 fee appeared at the bottom. I changed the duration back to 7 and it the fee went back to zero.  Why does this matter?  The item is down to $6 so it is hardly worth the extra dollar to sell it with the lower duration. Thanks!