802.11q expected for 3rd party devices, is this normal?

I'm wanting to say no, I hope.

Company I've been with for 12 years has been around for 15. We put "kiosk" see devices onto our clients sites, and often get to use their network as transport. Most common setup is site to site vpn between our DC and their, and a dedicated vlan that spans the site, terminated to untagged access points at the given locations and switches.

Had a client yesterday tell me they're shocked and disappointed that we don't support 802.11q tag support on our devices, as now they have to "manage the switches" and concerned about what will happen if someone repatches one our leads.

This is a coal mine, in full 24/7 operation. I'd like to think people aren't willy nilly repatching switches! Certainly in my 12 years, I've never had to respond to an issue where the cause was that someone moved our patch lead. (unplugged or cut leads, sure)

Is this a reasonable expectation?

Fwiw, our devices in this case are windows 8 embedded on an industrial PC, and some moxa IOLogik devices. I'd say I could probably have made the PC do it, if the drivers supported it, but the moxa flat out doesn't.