This kind of makes sense in the same way that AirBnb does. There are more users looking for work than employers looking to hire, just like there are more tourists looking for cheap accommodations than landlords willing to rent their space. The platform will cater to the group with the higher bargaining power.

However, the surveillance just seems like an absurd waste of resources. The author quotes $400 for the job, why does it matter how many hours it takes them? If you think $400 is too much, then bid on the project.