The process of choosing the best vegetarian caterer is similar to picking the best traditional caterer. You should be sure to taste the caterer's food before hiring the company. Get references for the caterer from friends and previous customers and study the caterer's resume. If previous customers had difficulty with the vegetarian caterer, you may have those same problems. Cost may be another concern, especially if you are on a budget. Other things to consider are the quality of the company's equipment and commitment to vegetarianism.
The best vegetarian caterer is one who has experience preparing vegetarian meals. You may want to select a caterer who specializes in vegetarian cooking rather than one who serves vegetarian dishes but also serves meat-based dishes, especially if you are concerned about vegetarian food sharing the same equipment as meat. Ask about the caterer's resume. Learn where she went to culinary school, why she cooks vegetarian food, and where else she has worked.
Ask friends who have hired a vegetarian caterer in the past for recommendations. If your friends or acquaintances have had problems with a caterer, you'll want to know that as well. Also look online for comments from previous customers to learn if the caterers you are considering are good at communicating, arrived on-time for their appointments, and did everything as arranged. Also ask the caterer to provide references.
Talk to the vegetarian caterer about the cost of everything before you make any decisions. Ask for an item-by-item breakdown of the cost. For example, find out if the catering company will provide glassware and dishes, and if they do, what the charge will be for each item. Also find out the charge for each entree, appetizer, and dessert. If the company is providing staff to work the event, find out the cost of that as well. You may only want a caterer to provide food, not staff or dishes, so you need to lay out expectations beforehand.
Sample the caterer's food before hiring one. Although references and cost are important, bland food is a deal-breaker. Ask the caterer to prepare a sample meal for you and taste it with others who are involved in the planning of the event.
Look over the materials the caterer will bring to the event. Ideally, the glasses, dishes, and linens will look new. If the glasses are chipped or the linens faded or stained, ask for new ones. The vegetarian caterer you choose should be willing to provide you with the highest quality materials.