I recently bought the following C5 on eBay, and went to collect it today - wish I'd never bothered!
http://www.ebay.co.uk/itm/262573551647
To start with the battery was flat, so he had to jump start it which did fix the power steering fault, the other fault mentioned I assumed was EGR related.
Sure enough, I noticed straight away that there were loads of parts missing under the bonnet:
The plastic engine cover
The air pipe from the air box to the turbo - so the air going into the engine was completely unfiltered
And the complete EGR system:
Meaning that the heater matrix hoses were disconnected (as they cool the EGR system down), which meant there was ZERO coolant in the engine - god knows how long there has been no coolant in the car - he says he's driven it in the advert!! This meant that hot exhaust gasses were literally pouring out into the engine bay. The hot EGR pipe that goes into the inlet manifold was missing, leaving a gaping hole. There was also a breather hose going to nowhere (see the breather in the picture below situated just underneath the number 9:

Absolutely rediculous - and there is no way anyone even slightly interested in cars would miss all that! And the scary thing was there was no check engine light on the dash, how I don't know??
Sure enough I told him this car was not as advertised and that I wouldn't be paying for it - shame I had spent £85 hiring a trailer to get it home.
Hopefully if the other person who was bidding against me see's this.