You can always require Mechanical Turks to pass qualification tests before they work on your HITs. There are also pre-existing qualifications like language and

You can always require Mechanical Turks to pass qualification tests before they work on your HITs. There are also pre-existing qualifications like language and location. Of course, you need to pay well enough to get enough people to bother, but I imagine one could build a reasonably skilled workforce for many areas if your training material is good and you have an objective measure of the correct answer. This image description application is both perfect and terrible for Mechanical Turk though - it's an ideal task for a human rather than a computer, but it's also impossible to score the result objectively, so you'll have to pay everyone, all the time, or introduce another level of scoring - "Is this an accurate description?" "Does this description read fluently in $LANGUAGE" etc.