I think if there's a delay in putting the agreements in place, that is a barrier. I think Canada is a good example. It's taking you too long from the time you sign an agreement to the time an agreement is ratified, and unless the agreement is ratified, you can't use it. There has to be a political will in countries to move from the signing towards the ratification.
Let me make one point on what the previous speaker said about informants. All countries use informants, and in a sense that's part of a citizen's duty. If you know that other citizens are evading taxes, you should actually inform the tax authorities.
This is not a new phenomenon. The scale perhaps has changed, but it's not new.