Watch for signs of this and offer to come back another time. Tape recorders are great, but they make some people very self-conscious. Be sure you have permission to tape an interview. If there's any reluctance, back off. The presence of an unwanted tape recorder may backfire in your face and you won't get anywhere near the amount of information you might have without one.
Camcorders are similar to audio tape recorders, but they tend to make the subject extremely nervous.
They are very distracting. If there's a reluctance or some sensitivity to answering a question, back off. Some memories can be very painful to discuss. Leave them alone. Also ask if you can call or visit again, perhaps to clarify any items discussed during this interview or to discuss new items.