My concern is that if I buy something from a retailer say from the UK or a state in the US that won't ship to NZ but will to YouShop and they charge me sales tax , YouShop then charges another 15% GST for the item again. Can I get the additional GST back or will it be tough double dipping??
YouShop address is a state with no sales tax. If you buy anything in the USA sending to YouShop you will not be charged sales tax, so no need to worry.