Hi Tomasa,
Clients (customers) can be a real pain, can't they? :)
First thing you need to decide is how badly do you want the business?
Next, is your refusal to meet in a restaurant likely to lose you the account?
Costs vs benefits.
Of course, you could always lie. Your doctor put you on a special diet, and you can't sit in a restaurant and keep it. Offer snacks at the office. Or don't.
Hope this helps.
Source: http://www.abusinessmentor.com