For your sales to customers located outside of the United States, we are not the retailer of record, but are acting as your "disclosed agent".  This means that you are selling the products directly to those customers. Value Added Taxes (VAT) may arise when you sell to customers in certain countries, and if so, you will be required to pay the VAT to that country's tax authority.  Your obligation to pay VAT may differ depending on the products and countries involved.  You should therefore seek VAT advice from your tax advisor on all sales to customers in the EU, including the UK. 

We recommend keeping the following points in mind when seeking tax advice:

1. Topspin does not pay taxes on goods outside the US (i.e., VAT) as disclosed in our Terms of Service and Topspin Support FAQ.
2. Artists should price goods in whatever manner they feel is compliant to taxes outside the US (we do not provide advice and recommend you speak to a tax expert, which it sounds like you did). For example, with respect to VAT, typically goods are priced inclusive of VAT and thus the retail price displayed at the start of the Topspin purchase flow and payable upon checkout should include any VAT. 
3. Artists will need to look at the monthly account statement and determine which sales occurred in which territories and pay any necessary taxes they feel they owe. All this data is available in the monthly account statement as sales are broken down by price, currency, and country code. 
4. Topspin currently does not provide VAT rate breakdowns in the monthly statement, but these can be looked up online and are available on sites like Wikipedia - http://en.wikipedia.org/wiki/Value_added_tax#Tax_rates