Kamaaoma, I can't help but wonder, wouldn't the car be storing error codes in the system computer that the dealer can harvest to diagnose the problem. I'm a little distressed myself at your situation considering that modern cars have done half of the diagnosis onboard when a problem occures before the vehicle even hits gets to the dealer.

So, in addition to what Georga suggested, demand that they give you a printout of the codes stored in the onboard computer, or at least document them on their work order for you. They should also explain what the codes mean. If you get turned away again, at least with the codes, you can go online and use Google or something else to search for those codes and see if they dealer is spoofing you or telling the truth.

It has been said:
Hybrid drivers come in 3 flavors, greenie, techie and cheapie. Pick any 2.
2005 Prius, Melinium Silver over gray, package 5 (AI)