Basically there are a few things you'll want at a bare minimum to check you
buy (and this still won't guarantee you'll get a system that is problem
free):
1. Make sure the system uses Intel graphics ONLY. No NVIDIA/ATI/Hybrid
solution.
2. The system is NOT an HP, Lenovo, Dell, Toshiba, Sonay, Apple, IBM, or
Acer. These companies are implementing digital restrictions on the mini PCIe
card slots where the wifi card goes. You won't be able to replace it with a
free software friendly wifi card and there is a high chance you won't get a
free software one as most companies are not shipping with free software
friendly chipsets.
3. I had a #3... but forgot what it was now.
There are a variety of issues you can still encounter like wifi switches that
don't work (ie system won't work even without digital restrictions as the
wifi is off-by-default and there is no GNU/Linux driver for the on/off
switch).
Other common issues are ACPI related. Things like the graphics, sound, and
power management being problematic or non-functional. You won't really be
able to determine if a system has these types of issues easily short of
having the system in hand. As someone else mentioned there are other
solutions if your buying a new or refurbished laptop: ThinkPenguin (ie CEO
here) and Gluglug sell Trisquel friendly systems (the later doesn't even have
a proprietary BIOS, but as they are based on much older refurbished Lenovos
there are problems keeping these in stock- don't think you can get one at the
moment- maybe in a few months).
