one thing i would add is that a "white plug" does not always make or break a deal for me.

i almost always keep plugs in my sump. so most often they are purple'd up well before gluing a freshly cut frag to them. but, i have also had to make a mad dash to the store to grab a bag of plugs just days before a swap when i realized i didn't have enough for the ricordia i had growing in a rubble container. on one hand, purple plugs with fresh cut frags .. on the other, white plugs with well established/healed corals.

my point being, a closer look will usually tell the tale .. and although guidelines are great indicators, they aren't absolute.

when in doubt, ask lots of questions!