I have set my website up to have flat rate fixed shipping, as I want to charge the same regardless of how many items, different or the same, that a customer orders - this is £3. The listings are all set up to "calculate for me using my shipping methods" so I would expect that whatever was added to the basket, the shipping would remain at £3. However, if I add a couple of items from one listing, then a couple from another the shipping increases to £9? I am literally pulling my hair out, so any advice would be greatly appreciated.
The same thing happened to me, you must have shipping on each item as well as flat rate shipping you will need to go into each product and click the tab that says calculate me for m shipping methods instead.