> You could farm it out to two people and if the results disagree, then payment is decided by a third. But then you've just doubled the (paid) workload, and you've not really solved collusion by a significant portion of the workers.

That would be the naive/bruteforce way to verify trust.

Just like you can find a substring faster via Boyer–Moore than a char-by-char match, there are more efficient ways to verify trust in a distributed environment like this. There's a few white papers on the topic.