I was fascinated to read your post, 'matdotcx'.I'm surprised it's taken this long for anyone to mention it, but, it's trivial to put a third party application onto a brand new Mac, out of the box, without user intervention.
All it takes is one reseller to mistype a serial number into Apple Business Manager and the machine will, on first boot, connect to someone's MDM service, pull down a configuration profile, and do its thing.
In the past, we've deployed systems have have been mistakenly attributed to other organisations' DEP instances, and our employees have been greeted by internal tools on the desktop for a company they don't work for. It's not unheard of, but it's certainly a lot more likely than a refurb system ending up in a new machine's box, or someone doing a interception of your friend's machine.
Sadly as the machine is now gone, there's no way to tell if that was the case, but I'd bet a dollar that was the cause.
Can you think of any reason why anyone would wish a new computer to have ClamXav installed upon it?
Btw, the machine in question is NOT gone. It is owned, still, by 'Joe C' in South Carolina. Most folk think he should ask Apple to exchange it for a new one. Is it still possible to ascertain evidence of what transpired? Post #38 refers.
What are your views, please?