I've never heard of them doing this, though I have only used this twice in several years-- once because an espresso machine stopped working right after the original warranty expired and once for a router which failed. I did figure out that the router failed due to a faulty power supply and I asked AMEX to just reimburse me for a new power supply, but they just wanted to process a refund.

I can't imagine they would be happy refunding you for a change of mind after 60 days, but if you are a high enough volume customer, perhaps they would let it go. I've only used it because the item went bad, so keeping the item isn't helping me all that much. I suppose they would be well within their rights to terminate you if they found you were asking for lots of refunds, but I'm sure it's all weighed against how many fees to generate for them otherwise.