Tell them to keep it but delete wireless profiles and turn off wireless?
Exploitable 3DSes are always good fun for science and testbeds.
What can you actually do with a 9.2 system without internet access though? You can't install Ninjhax and you can't enter the gateway menu.
Sure, you could turn wifi on briefly, but just look at how many people have accidentally downloaded the update nag, particularly before we knew the trick to deleting them. My feeling is, if some people screw up and draw Nintendo's attention, it could end up hurting everyone else. Better to give guidelines that don't allow for accidents.
For what it's worth: broken Old 3DS's really don't go for that much: http://www.ebay.com/itm/Nintendo-3D...856?pt=LH_DefaultDomain_0&hash=item1c5103a5e0
Searching past eBay auctions for Old 3DS's that actually sold (got at least one bid) this was the most recent one I could find, and it's actually still quite functional—it can connect to the internet and everything, just not read game carts.