A bit late to the topic but having been a cobbler for 15years prior to my current career I can assure you dog skin is unsuitable for leather and cat is too small making it too labor intensive (expensive) when there's whole pig or cow available.
The fur however is often used as liner and adornment like you see on the hooded puffer jackets, but in the EU has to pass inspection and be honest about it's origin.
Leather is fairly easy to tell apart by traits like structure, elasticity, pattern of pores (dogs don't have pores which is the main reason why their skin is useless), tear resistance (north African goat is always distinctly easy to tear and the smell never really goes away) and line pattern (look at the palm of your hand for example).
Much European cow leather is good quality thanks to electric wire fences, whereas Argentinian cattle often shows scars from thorn bushes, parasitic insects and barbed wire fencing.
I'm sorry it's late and I'm rambling instead of sleeping.