No info on Costa Rica, but even Canada used to charge full duty on tools you brought in from outside. It only happened once, I have no idea how they determined that you were not coming back with different tools. As far as the thinking on that goes, when you come in you are taking the work from a local who did have to pay import duty on tools he uses in his business, unless the country in question makes all it's own tools, which really doesn't change anything.
Many is the time I have traveled through the US from one point in Canada to another, and they never gave me any trouble about a truckload of tools. But come in through an airport and it is a different mater.