The biggest headache selling in the US and Canada is Amazon's insistence on quoting four-week shipping times from the UK, even though airmail will make you much faster than that in reality. It puts a lot of US and Canadian customers off. The obvious answer, you would think, is to use FBA but if you do that, you will become liable to pay taxes to the state governments in those states where the fulfilment warehouses are located. That's almost impossible to do because, even though you will know what fulfilment centres Amazon asked you to ship product too, you can't always tell which centre fulfilled which order. Amazon often split the same inventory item between two or more warehouses, so when you make a sale, how do you know which one fulfilled the order, and hence which state government are owed the tax? Answer: you don't.
If you are not going to do that, i.e. you will fulfill orders from the UK, you realistically need a returns agent located in the States or Canada because without one, you will be expected to pay the shipping costs of all returns, regardless of the reason the customer no longer wants the goods.
I'm not trying to put you off but I do think prospective sellers in the States need to be aware that it's not nearly as simple as you might think, and definitely not easy to do with any success. I know because I've been trying for years, and basically getting nowhere!
