Google is definitely a trusted source, however, they're a monster in size and that sometimes leads to the inability to contact them should something come up.

I had a pretty severe Gmail problem once and I remember trying to contact someone or report the issue, a nearly impossible task. All I found were static help documents. Of course, that was ~4 years ago. And their support for Google Checkout may be handled entirely different from that of Gmail, but it's still something to consider.

Then again, I got burned by the Chargify pricing hike recently, so I can't really advocate to go with the smaller "Chargify-ish" companies, either.