I like the idea about the secret word Charles, I will have to try that next time.
The problem with freelance sites like Guru or Rentacoder is that developers just bid on anything they come across. They only get selected maybe 1 out of 10 bids, so they just make as many bids out there as they can.
If they read every project description word for word they would spend all day reading leaving not much time for anything else. So they just ballpark their bid based on your estimates and go from there.
If it turns out the developer made an error and under bid, you won’t get free work; instead you will get a very poor or incomplete job.
Every time I place a project on Guru there is one company that I know bids every time and they always bid the same amount no matter how big or small the scope is.
If you are lucky enough to find a quality company that you can build a relationship with going forward I would recommend giving them a nice bonus at the end of the project. They won’t forget it and they will definitely go the extra mile for you next time.