Your Scroll can accept MicroSD cards up to 32GB in size. Most reputable makes have been reported to work.
When inserting the card into your Scroll, please don't insert it at an angle or it will disappear into the inner workings of your shiny new toy never to be seen again - unless you have the required skills to take it apart and retrieve the card.
Personally, I would avoid purchasing a card from the well-known auction site unless the seller has a good reputation, some of the larger size cards have been known to be 4GB ones that have been....um.... how do I put this.... reconfigured.