Royalties different from the ones you see displayed on the Sell Your Images
page are due to various factors.
The most common explanation is the actual credit value per each package a buyer purchases. The more credits the package has, the lower the price/credit. Each credit's value and hence royalties are now calculated at the real value paid by the buyer.
For example, 8 credits purchased with the $9.99 package, will bring the contributor a reference of $1.25/credit: the royalties for a 8 credits image will vary between $3 (non exclusives, level 1) or $6 for exclusives. A $99.99 credit-package will bring the buyer 108 credits, which translates into $0.93/credit. Royalties for a 8 credits image are $2.23 (non exclusives, level 1) and $4.46 for exclusives. Add to the above the possibility of having third party downloads through our alliances
or the value of withholding taxes
for non-US contributors and you will understand why royalties values are so diverse. The price per credit PPC can also be affected by seasonal promotions and discount campaigns.