Would you rather have one set of rules for trade that you have to deal with, or thirty different potentially incompatible ones, not all of which are translated

Would you rather have one set of rules for trade that you have to deal with, or thirty different potentially incompatible ones, not all of which are translated into English? Unfortunately, neither of those things happens consistently the way you might expect. One of the big problems with the EU VAT changes for digital services was that suddenly instead of just knowing your own country's tax rate and being able to apply it throughout the EU, you had to know each member state's tax rates and in some cases their oddities around things like invoice formats or special classes of products or services that carried different rates. In other words, those changes did essentially the opposite of what the EU is supposed to do. Going the other way, if treating the whole EU as a single entity also means you can't offer products or services at different prices based on the widely different economic conditions in different member states, that is a large and entirely artificial distortion in the market, and it's a policy with questionable social and economic benefits.