Let's assume that the CRO expert makes changes to your web design and copywriting that cause a very modest 20% upsurge in c/r taking it around 1.8%. That means instead of generating 75 sales every month, you'll now be generating 90. But unlike PPC where your additional sales will disappear the moment your money runs out, conversion rate optimisation continues to generate an additional 15 sales per month through the year.