Heather Oberdorf (plaintiff) bought a dog collar using Amazon.com Inc.’s (defendant’s) Marketplace. Third-party vendor The Furry Gang filled the order and shipped the collar. Oberdorf put the collar on her dog and clipped a retractable leash to the d-ring. When the dog lunged, the d-ring broke, and the leash snapped back, hitting Oberdorf’s glasses and blinding her in one eye. Oberdorf sued Amazon for negligence and strict liability. Neither Oberdorf nor Amazon could locate The Furry Gang. Amazon requires vendors to indemnify it and provide product warnings, and Amazon retains the right to reject vendors, but Marketplace customers cannot communicate directly with vendors. The trial court granted summary judgment for Amazon, reasoning it did not qualify as a seller under Pennsylvania products-liability law. The trial court also found that the Communications Decency Act (CDA), which precludes liability for publishing third-party content online, barred Oberdorf’s claims. Oberdorf appealed.