I suggest, u bring along ur motherboard or the measurements
during ur casing hunting. Because SFF till now doesn't really have
a fixed form factor, some use Micro-ATX, some use ITX, some use
their own form factor.
The problem with this is, ur motherboard may seems to be able to
fix in but u might find later on that the mounting holes within the
casing might not match, that is why I suggest u bring along ur
motherboard.
Please also note, some equipment might not able to fix in, such as
ur CPU heatsink and PSU. U may need to purchase one that is able to
fix in. (sometimes even ur video card, those with big
heatsinks).