Caller: Hello, I'm ___ from ___ agency. We contacted you by email last month about translating some automative material.
Translator: That isn't my area of expertise.
Caller: What is your specialization, then?
Translator: I specialize in academic translation, especially in philosophy.
Caller: OK, if we have something in that area we'll get in touch. We won't bother you with automative material again.
This is why it's important for both sides, the translator and the customer/agency, to be aware of specializations.
As a translator, you must choose not only your languages but a type of material to specialize in. I always feel my heart sink when a translator, usually a young one, tells me he or she translates "everything" in a particular language pair. Nobody is an expert in "everything", and even highly educated and fluent speakers of more than one language are not equally skilled at all the possible types of material written in their languages.
Other professions have very clear sub-specializations. You wouldn't ask a plastic surgeon to deliver a baby or a tax lawyer to handle a divorce. I would like to see translators choosing a similarly narrow definition of their expertise. Less is more! Saying you specialize in translating a particular type of texts makes you an expert in that specific area.
Translators should have a clear "introduction" to use when they meet someone. It could be something like: "I translate from [source] to [target], and I specialize in ____". It is also important to list specializations on your own website and anywhere you have a professional profile.
Customers and agencies should also be aware that translators have specializations, and should find out what a translator specializes in before (online) or during the first conversation, and then offer only appropriate work.