[justinwi]

I didn't use masters for mine because it was easy enough for me to look at the email addresses that were coming in and see if they were junk.

Would be curious to find out if masters will work for $.05. Please keep me posted! :)

[seeingfurther]

In 2 hours I had 2 HITs completed by masters. Probably going to need to switch to regular workers and closely monitor like you did.

[Chupachupski]

One approach is to get each hit done by two (or three) regular MTurkers and crosscheck the results. I've seen this done with "human OCR" type tasks.