What Do You Do When Outsourcing Goes Bad?

Xphox wonders: "Recently we have been referred to an outsourcing company to finish customization on a script that the author had no time to complete. Everything was going fine until recently. At what point do you consider they may have just ripped you off, and how do you know when to file complaints and withhold payment?" "I have been working with what I thought was a reputable outsourcing company, referred to me by the author of the software package. We agreed that payment would be made once everything was completed. After a few missed deadlines, the project finally seemed to be finished. The only thing left was a small bug fix, and an install script which needed to be completed. As agreed, he delivered the install script, and we made the final payment. Upon testing the new install script we noticed things did not work as intended, and all attempts to contact the outsourcing company has resulted in the following answer:

'My guys are still working on it.'

My fear is that if I don't act now, I will not be able to recover any funds, and will be stuck with a product that is useless. It has been 9 days since I've received an email from them, and I'm starting to think I've just been taken advantage of. Since the script is protected with Source Guardian, I am unable to finish the modifications myself."