I'm not sure if this is old/repost, but i couldn't find anything with a quick search so here it goes. Maybe this is just for lower levels and is intended if so, I'm sorry for wasting your time.
When I was leveling up skinning on my new character in the barrens (haven't tried other zones) I started grinding and skinning, except I didn't really care for the leather so I left it in the body and went to another mob and did the same. When i had a pile of like 9-10 mobs in a small area, i went back to the first mob that i killed and used the skinning skill from my spell book to skin the mob, and to my surprise it gave me another skinning level. So i tried the next and the next and it worked, but if i tried to skin the same one twice with in a short amount of time it didn't give me a level. So there is probably a 1-2 minute cool down on getting another level from a mob. The only problem with this trick is that after the first time u skin it and leave the leather, someone else can come and skin it and take it.
I would appreciate if I could get a quick response so I could change the topic to being more of a tip rather than an exploit, thanks.