From the Amex website:
Return Protection: If you try to return an eligible item within 90 days from the date of purchase and the merchant won't take it back, American Express may refund the full purchase price, up to $300 per item, excluding shipping and handling, up to a maximum of $1,000 annually per Card account, if you purchased it entirely with your eligible American Express® Card.
Purchase Protection: When something you buy is broken or stolen, it shouldn’t be your problem. That’s why if you use your Card for eligible purchases, they can be protected from accidental damage or theft for up to 90 days from the moment you buy them.
For platinum cards it's: accidentally damaged, stolen, or lost