Firstly, welcome to Cheftalk.
Meez is right here.
This is a timely topic at the moment here on the threads.
It is very disconcerting when someone else purchases the food for an event you have been hired to cook and serve.
How can you know that the quantities will be correct?
How can you be certain of its quality?
Your reputation is going to ride on all that you do here
If you run out of food, that would be terrible.
Ultimately you are in charge and you are responsible for this event.
Does not matter who bought the food, to the guest, you would be to blame.