if ebay was the only thing moving down, you'd have a valid question. its called consolidation, the market is taking a breather. ebay had been up 25% over the last 3 months, i dont think theres much to worry about.
if you look at the chart for the last year you see several pullbacks, especially withing the 10 days prior to earnings. I think ebay will continue to outperform the market through the end of the year and took this opportunity to add.