Rediculous cost for a 10mm scratch.
Looking at the quote it also includes amounts to get the car back to 100% condition, not the condition it was in before the accident happened.
Theres a lot more damage on that quote than the damage which may have been caused by him hitting it with this bike.
£275 for the stripdown and spray, £150 for the paint, £40 for stickers (taking the p***), £100 for a specalist ??? +Vat
£664
Its difficult if its someone you know rather than a stranger in a carpark.
Dont pay any money until the work has been done and the bills been paid.
She'll think twice about having to pay the difference herself, and maybe wont get the work done anyway.
On the other hand get her to claim it on her insurance. Thats what its there for. She probably wont, as her premiums will go up and its not worth it for a 10mm scratch. I'm sure the insurance company wont be interested in claiming the amount back from your friend due to the hassle.