I found this listing on ebay for a xbox 360 repair service http://cgi.ebay.com/Xbox-360-Repair-Servic...1QQcmdZViewItem. Has anyone tried these people for xbox 360 repair? they say they will add a extra heatsink and reball the gpu. Should i try them to fix my 360?

I would be very wary. there are many people claiming to professionally repair 360s. Many advertise re-balling etc, but most will not have the correct (expensive) equipment to do the job correctly.
What you end up getting is a hot airgun fix with and Xclamp fix thrown in. When the system fails 3 weeks down the line, it can prove impossible to get it sorted.

Did you try them ?