Apart from the ethical issues raised by these platforms (detailed in (Fort et al., 2011)), microworking platforms do not support true training of the workers: tests can be set up to select them, but they have to perform hidden work to train themselves (as shown in (Gupta et al., 2014)).
tasks must be simplified to be manageable by workers: for example, a task related to recognition of textual entailment across several sentences (which might actually reflect entailment, neutrality, or contradiction) could be simplified by presenting only one pair of sentences and a binary response to a single question, such as "Would most people say that if the first sentence is true, then the second sentence must be true?"