Used that green shimano grease on my BB & the excess has stained my frame!
1. The most important thing about buying a new
bike is to make sure it fits. The only way you'll know if the bike is right
for you is to size up the bike and make sure that the bike's geometry matches
your body's geometry. Ask questions and do some research.
2. If possible, try to find a shop that will
let you demo the bike on real dirt. Five minutes in a parking lot won't cut
it. You wouldn't buy a car without a real world test drive, and a bike should
be no different.
3. Don't belive the hype. Just because
your favorite rider or best friend rides a certain bike, that doesn't mean
that's the best one for you. Have an open mind and be realistic about your
needs and ability.
I don't have any personal experience with stains on carbon but try some car wax and a microfiber cloth. I have a feeling that would work (if it doesn't remove the car wax with rubbing alcohol so it doesn't coat over it making it harder to remove). Another thing to try could be WD40... and if all else fails try Mr. Clean eraser cleaning pads (basically a 2200+ grit wet sponge).
seriously, carbon is pretty tough. Even the resin is not easily broken down. Remember this is a space age material. In fact, its so tough to break down that there is no real way to recycle it. Most of it just gets landfilled. So most solvents won't really hurt the carbon at all. Now the paint is another story.