Size of advance = muscle behind publisher's marketing efforts... makes sense. (buildbookbuzz.com)
You can negotiate the size of the advance, the interest rate, the length of time clients have to pay, their reliability, and any ancillary fees the institution might charge such as minimum payment amounts, invoice processing fees, mailing and lockbox fees, credit reviews, overdue fees, and so on. (due.com)
They are influenced by a variety of factors, including relationships with authors or literary agents, size of advances, potential sales, future of a series (if there is one), competitive titles, size of potential readership, and how promotable a book or particular author is. (citybookreview.com)