http://journal.sjdm.org/10/10630a/jdm10630a.html
Effectively, without the bots, the paper contends that the Turkers are at least as representative a sample as undergraduate students.
Personal anecdata: I took many MTurk surveys for about a month in 2012. It is mind crushing work.
There were countless near identical surveys presumably by psychology undergrads.
Pretty much anything in Kahneman's Thinking Fast and Slow was there.
Very quickly you recognize the typical priming experiment and then is your response any valid?
If you know the idea behind the baseball bat and ball pricing question then is your correct answer made in a split second helping?
Most survey givers wanted MTurkers with high ratings.
If you think about it, those MTurkers with high rating would have likely seen all those survey questions already.
Thus experienced MTurkers would really distort the answers compared to a random sample of undergraduates.
Maybe you can compensate for that somehow.