Why would you like to keep non-lemons ? Is this a trick question ? You'd want to keep the good candidates for the same reason you started a hiring-process in the first place: because you're in need of more qualified employees. (and most of the time, you'd prefer them -now- rather than in a decade)
Furthermore, your requirements, or your job-market, or both, may be such that the supply of non-lemons is limited. If you've had the position well-advertised for half a year, and 8 people have applied - one of which is an actual good fit, then rejecting him may mean spending another half-year looking for a suitable candidate.