Well said above
Waves are expensive plugins, so maybe the solution is to look at other brands. There are few Waves plugins that can't be replaced with others. I like Waves L2, but Massey's L2007 works nice at $89. Waves reverbs are okay, but others will match or better them for less money(Breverb, TL Space, 112db Redline and IK Classik reverbs come to mind). What do you need? We'll find a cheaper alternative.
and yes, I have bought used plugins, both on ebay, and in the buy&sell section of the DUC(got a good deal on a Waves bundle). Check that feedback as the only stiffing I got was from an ebayer with low feedback(sent so-called legit plugins on a CD-R with no numbers). Always ask if it is original install disks, or if its an iLok transfer(you can download all Waves plugins from their site, but you need an iLok to make them work). Many other plugins use an authorization code(like IK and Massey).