Have to agree with Bradders here - ... See below
You must include a price in your for sale or trade post
You cannot increase your asking price
You must include the P&P charge to UK. If not stated separately it will be assumed that it's included in your asking price
Imported (non-UK) goods must have their country of origin stated
Accepted payment methods must be stated
I know you wish to be fair as possible but you do need to firm up a price .... Best of luck with the sale.... Not that you will need it they will shift pretty quickly.