A lot of fun things in this thread to talk about.
Firstly the paint, if it feels like frosted glass and sounds like sand paper it's heavy contamination, the liquid removers won't work and I'd personally just skip the mild claybar and go straight to a heavy one and if it's the entire car safe yourself the hassle and get a clay mitt to make it faster because claying in boring!
As for using a clay bar - I’ve clayed cars I’ve owned with good success (admittedly, I’ve never done a brand new car though where the paint may not have fully hardened). IMHO provided a mild clay is used with plenty of lubrication (I use a quick detailer), and the outside surface of the clay bar is folded to the inside regularly so the surface of the clay that’s being applied to the paintwork is always clean, there’s little risk of marring or inflicting damage.
As SRGTD said lots of lubrication helps to reducing marring or damage, I just spray snowfoam on top and use it after it's been washed as it's also lubricative, but it's important to note claybars are an abrasive tool, and will add swirls to the paintwork so you always want to follow this up with polishing or a filling glaze.
As with the Sales Manager said detailers are fanatics, of course we are!
If we weren't you'd get the same standard he delivered the car in! A £600 detail isn't for Lamborghini's it's for any car as I speak I have a Skoda VRS in for one, for all that you want from the car a maximum of £200 would get you 95-95% of paint perfection.
That being said the way they delivered the car is not on, but realistically they've saved you hassle as clearly they don't know what they're doing with bodywork and would've risked more damage than good.
I'm all out of C2V3, so will have to buy something else
Gyeon WetCoat or Koch Chemie So.02, you'll thank me later