What I did was to have up to five person work on a hit. Many simple hits are done at 0.05$ so it's still not too expansive.

For text submissions, you can enforce validation rules (simple and regex). So you don't have to manually reject non-conforming work. You can also have the Turker fill in their work on a webpage that you control, so validation can be much more advanced. I never went all the way but sometimes I think about it.

From what I read the standard technique seems to be let two people review everything. When there's a discrepancy you can add more manpower (and take the majority view or so) or look at it yourself.

Hey ashishk, sorry for using HN to contact you, but I can't seem to find your contact info anywhere.

Our company provides very affordable and accurate photo approval services. Photos are manually approved and we can handle anywhere from 10-1,000,000 photos per day. If you're interested, feel free to email me (email address is in my profile).