Being a 'bestselling' author or having a 'bestselling' book implies a high level of success and recognition in society. After his book became a bestseller, he was frequently invited to literary festivals.
Pro Tip 2/3
Context Specificity
'Bestselling' refers to high sales within a specific category, like novels, or within a specific time frame. Her cookbook was the bestselling in its category last month.
Pro Tip 3/3
Not Always Quality
A 'bestselling' item isn't always the best in quality—popularity doesn't equal excellence. Even though some critics panned it, the album was still a bestseller.