Identifying device type remotely

I am writing an IP scaer in C#... I'm not looking for coding help, but rather the how do I determine the device type. Using WMI and remote registry I am able to get all information I want from desktops and servers. I can also get the device MAC address and vendor but type is stumping me. By type I mean simply "Printer" or "Desktop"

I tried using nmap on a printer and desktop like so: nmap -O ip_address but it retus device type "general purpose|phone" on all of them. I was able to use this to correctly identify the smart switches, though.

All I want it to retu is something like "Printer" or "Desktop".. Is there a reliable way to do so using any means?