>>75448I got in very easily actually with a one-way ticket. Then again I was wearing a suit and I spoke japanese to the customs attendants. There were no questions asked, beyond the cute customs girl wondering what I was doing, to which I simply explained I'd be having a nice long vacation.
You shouldn't have any problems if youre from the US or (major) EU and you look presentable. If you want a cover story tell them you are in town to give a business proposition and depending on whether or not your client accepts or declines, you are not sure when you will be leaving. Be sure to have the right info, etc.
Good luck.