I’ve always been cautious about claiming to be an expert during an interview. The expectation of most hiring managers is that an expert knows everything there is to know about his area of expertise and that there is nothing about his specialty that is unknown to the expert.
The practical reality is that most people don’t know everything there is to know: not even the experts know everything and even when they have the answer, the solution may not be what management wants to hear.
Experts only know more than most other people.
What do you think? Would you claim to be an expert on your resume? During an interview? On the job?