They are usually successful or famous writers.

They leave their contact details in social media
seeking people to purchase their books.

However, other than that consideration,
they have a coda:
'  Due to the large number of mails I receive,
   I'm unable to answer any nor do I entertain
  unsolicited mails'

This is hubris to a stinking extent
and also totally lacking in grace and humanity.

Thus, I refuse to purchase their books.

The talents of such people shouldn't make
them feel they stand apart from others!
A famous Chinese proverb goes like this:
Chiang-chong hai-yu chiang-chong sow:
You are strong(or smart) but there will be others who are stronger (or smarter!'