You've got to realise that very often as a supplier you are fighting a battle you can't always win. You've got Allmakes/Britpart/Bearmach in one corner, PayPal/eBay/banks in another and DHL/Royal Mail etc in another.
It only takes one small thing to go wrong wrong in the supply chain and the customer shouts at you.
Regarding the pricing, I have absolutely no idea how Island4x4 sells parts that cheaply. I know that the quality can be poor in places but most of their stuff comes via Britpart or Allmakes. My aftermarket parts supplier can't sell me parts (trade) as cheap as Island sell them (retail).
Anyway, you've not been happy with a supplier so walk away and try the next. I believe p38spares is one of the better customer orientated ones.