Unlike in America, in Europe you are allowed to have as many agents as you can get to represent you. Having many agents working for you is very important as it is always better to be sent by an agent to a house audition. However, it is risky to rely on the representation of just one or two agents because an agent’s contacts and knowledge of available house auditions could be limited. Also, if you write to and audition for only a few agents expecting one to find you work, you could be disappointed. If you are just starting out, have little performance experience on your résumé, and your fach (voice type) is not that marketable (i.e. you are not a tenor, or a dramatic soprano), you may find it very difficult to get even one agent to help you.
As Rick Hartung (president of Hartung Artist’s Management in New York City and the American representative for the International Opera Center in Zurich) states: “Since agents are very selective due the abundance os available talent-including their own roster to be taken care of, it becomes necessary to audition for as many agents that can be fount with the object of any one of them arranging for specific auditions. (The New York Opera Newsletter).
Thus logically, the more agents you write to, the more you increase your chance of finding more agents to represent you and to find you work.