Richard Mellish wrote -
"Singing for an outsider who is visiting partly or solely for the specific purpose of collecting is significantly different. The extent to which it is an intrusion depends on the personality, skill and attitude of the collector."

Exactly so! I can remember feeling very uncomfortable in the audience of a concert where a prominent singer talked about a ballad that he had recorded in recent times from an Irish traveller. He sounded very pleased that he had acquired this real gem but I felt that in the process of obtaining the song, the poor informant had been hounded and stalked.