Vectra Problem

[Cammie]

My V/Vectra 2.2 SRI 150 Started running quite rough,I put it into a Vauxhall Dealer for Diagnostic check which showed up nothing(NoFault lights on Dash) they have now had it for 2 weeks,and have just told me it is ready to pick up.They have been going through a process of Elimmanation, I.E. fitting Various parts without success,I think these parts are going to form part of my bill along with labour which may be as high as �1100 or even more.Can anyone tell me if they can charge for these parts if they were not the cause of the problem.Where can i get good advice on this.Cammie