[wilfra]

It is not a non-starter for those reasons, it may just require some modification if they become problems or if it is deemed they are obstacles too big to even try to overcome.

When getting instant, reliable cash is the result, people will jump through an enormous number of hoops - and even pay money themselves the for opportunity.

For instance, you could require users to create an account on mturk and/or w/ the mturk shop so they can be tracked. If it is simple to do and prompted it should be fast an easy. If they can't even figure this out, they probably aren't qualified to be doing the work anyway.