I have found it best to scour the listings for items like yours. I sold a Sloomb cube here & apparently because you can buy them at Sloomb for $10 me asking $12 was not good. No stores sell them with free shipping so it is custom to list them at $12.50 to $13.50 on the Sbish B/S/T board. Here, nope, not so much. Buyers don't care what your pp fees or shipping costs are. They see they can get XYZ for $XX.xx there so they don't want to pay your price if it is more than the going rate.
This is just my experience though (and if you see my feedback you can see I sell quite a bit). I have even sold quite a few diapers in the past 2 weeks. Probably close to 20.
Jodie ~ mama to Big K, Medium K & Lil' k