[solicode]

It's good knowledge to have before going to Japan, but encountering a Japanese person who would actually be offended if you were to offer a tip would be quite rare, I think. They're well aware tipping exists in other cultures. And they don't expect you to know the Japanese way of doing things. It could be interesting to see how they react if a Japanese person were to attempt it though. :)

Also, you could say a form of tipping does exist in Japan (kokorozuke), though it's quite different than what we usually think of tipping. The biggest differences being: 1. It's sort of a way of saying, "Sorry for the trouble" rather than "rating" their service. 2. You give the "tip" beforehand rather than afterwards. And it's likely you'll have to insist that they take it.

You can see this custom in high-end ryokans for example, but even then, it's not required or anything.