Second-hand beer ... huh?
Cost is always an important consideration when buying second-hand glass. New stuff can be difficult to negotiate. It usually is what it is, unless you go grey-market. Then all warranty bets are off ... and you are effectively looking at second-hand glass with nearly brand new prices!
I would suggest using second-hand glass for those who are beginning ... and be ready to grab a new and better version if the older one simply does not meet your needs. You can always sell it or loan it to someone else and let them enjoy it, too. :D
f/4 is a tolerable fixed aperture, if you have a good flash to accompany it. Buy the flash new ... second hand flashes notoriously do not last long. :cool: