One of the best aspects of living in Japan is the honesty and integrity of Japanese people, and as a general rule you can assume that people here will be worthy of your trust. One of my first experiences in culture shock here was going to my local Seven Eleven and seeing a brand-new car in the parking lot with the key in the ignition, idling away while their owner ran in to pick up some Pocky or whatever -- the idea that anyone would be so rude as to steal the car just doesn't enter into anyone's mind here. The food court at the Costco that opened in our prefecture can get quite crowded, and I've observed people saving a table by placing their wallet down as they go stand in line for food. At our local home center, when you make a large purchase of lumber or furniture the store will lend you a light truck to drive it home for free, with the employee handing over the keys without even taking a scan of my drivers' license (and me a foreigner). A friend of mine managed to lose his wallet no less than four times in different parts of the country, once as far away as Kyoto, and all four times the wallets were delivered to the police with cash intact. There is crime in Japan, to be sure, and bad people here just like everywhere else, but by and large I've been happy with the honesty I've encountered during my time here.
One of my favorite things about the Japanese is their tendency to be honest.