We were holding my mother's 90th birthday celebration a couple of yeas ago & wanted to have it a her favourite restaurant in Montreal.  Approximately 35 guests, mostly from out of town.  The menu selection was agreed upon - appetizers & dinner cost approximately $150 - $175 per person + taxes & gratuities - plus champagne, wine & liquor (open bar) - a considerable amount.  We were willing to pay for dessert - no problem, but wanted a special Tiffany cake that could accommodate the families' allergies, which their desserts could not.  In addition, this was a professional cake, made by one of the top patisseries in Montreal.  The reason for Tiffany - my mother was from New York - it was one of her favourite stores - & her special presents from her grandchildren were coming from Tiffany's Canada.  The response from the establishment - no. 

We declined.  Fortunately our home is large enough that we were able to rent a tent for the backyard and cater the event. We have not gone back.