Question: Who is the world best selling music artist?
Disambiguated questions and answers: question: Who is the world best selling music artist as group?
Who are the world best selling music artist as individual?
answer: The Beatles
John Lennon, Paul McCartney, Ringo Starr and George Harrison
Natural Questions answer: Elvis Presley
The Beatles
Rihanna (from the Wikipedia article "List of best-selling music artists")