Selling? No way. The wizard weakens himself.
I envision a wizard who's almost entirely self-centered; maybe not using "black magic" but one who doesn't much care about other wizards, or "weakening" them. They could easily have built in personal safeguards, so they specifically weren't weakened... embroider the armbands with gold thread for the runes, and use the same gold thread in one of their own offensive focus-items, enchanted to bypass the defenses of the arm-bands.
Also, smart wizards know how to bypass those defenses. Someone shows up sporting the armbands you made? Don't even try to cast a spell on THEM, just
forzare them a faceful of keys, or One Woman Rave them into utter confusion then gut-stab them, or whatever... ;-)
... Whamp subverted? seems unlikely ...
Seems entirely-likely to me, but YMMV.
Consider, though: Inari Raith -- with zero predatory experience -- almost got Harry. He feels that Whamps are an
entirely-credible threat to him, and to wizards in general. Margaret LeFay (no pushover!) was seduced by one. The Blackstaff apparently feels an especially-deep hatred towards them, presumably having suffered some grievous wrong.
... Stolen? I gotta think stuff like that is held VERY securely, but this one could be ...
While I
do think that Whamps could be an incredibly-potent uber-thief sort of security-penetrating expert, I was envisioning it in a more opportunistic fashion -- wizard is disabled? Swipe their stuff! Wizard in the field, but not fully "equipped" (wearing) all their gear? Swipe it while their back is turned! (I keep noticing Harry drop items in his duster pockets, and thinking "dude, a regular pickpocket could probably take that from you, and a magically-graceful-and-subtle one with a century of practice... you'd never spot it!")
I think the Deeps were likely simple mortal work ... Heck, the Whamps can seduce a couple of electricians or stagehands to rig this all up simple.
Harry was impressed at the system's durability in the face of his magic (I don't think "a couple of electricians or stagehands" could have produced that). Molly's (Svartalven-built) place was, IIRC, the
only other place we've seen that had "Harry-resistant" lighting, the kind that is noted in the text & called-out as "this is impressive and unusual."
... The Whamps are not envisioning magical duels happening much ...
I expect the Whamps were planning for all manner of "unlikely" contingencies. I expect they considered White Council wizards as among the
more-likely of those contingencies.
... Harry is not blowing up streetlamps and making cars freeze in place every time he walks near one ... Where Harry LIVED, even continual low level emissions can toast stuff. But he didn't blow up his office. Or the others in the building...
Yeah, Harry can walk by ordinary electrical stuff without hexing it; electronic stuff, not so much. He can't even carry a credit-card without wiping the mag-stripe on it. But he could walk into the precinct and not blow the lights; just not approach any computers.
My point, though, isn't the "ordinary circumstances."
Harry was afraid for his life; even worse, for his brother's life, and Murphy's (in the later incident, Carlos'; and hugely angry about the murdered women). And he was letting loose with his Kaboom magic.
This is gonna blow the tech.
Your average "electrician or stagehand" simply cannot build a system that will survive being in the same area with an angry, magic-flinging Harry Dresden.
