Remember that contract killings are only a part of an assassian's purview; an assassian can and often does accept regular adventuring work, quite often masquerading/advertising as a thief so that she can develop contacts, wealth, and a cover identity.  Particularly canny assassains will hire other assassains to masquerade as them in their cover identity to give them an alabi should a proper hit go sour.  Every so often, multi classed assassains will instead adventure as their secondary class, just to create even more confusion.  ("How could you suspect me?  I'm a frakking PRIEST!")