You have three charges of sharpen your knife.
So if you want to get a lot of rare skins, please try the great stormfang mob, isle of dorn just north of the theater event. The great stormfang is the skinning equivalent of a rich node.
What a lot of people don’t understand about rich nodes (and Seam and EZ-mines) is that they roll several times. Rich nodes roll the main herb/ore/skin twice and because of that they can roll finesse and perception twice as well.
If you use sharpen your knife on these it will give twice the rare hide drop. Similarly using perception or finesse boosting skills like mulch for herbing is multiplied by the multiple rolls on rich herbs.
A second place to look is rares, but only once a day. When skinned they are guaranteed to drop rare hides. I believe elites have a higher chance but not guaranteed.
And last your big summon, your once a day summon, is also guaranteed to give rare hides. You do not need to sharpen your knife on that. It will always give you a rare hide.