Social networks are a very good way to get more sales, but I agree with @jonbaas .
I’m active on twitter by sharing my past works very often. I don’t advertise directly on my gigs, it’s a waste of time. I advertise on my work only.
Sharing directly your gig on a social network is quite agressive and , it only shows one thing: “you have something to sell” while social networks are more “you have something to share”
For example on twitter people tend more to retweet a good artwork than a simple advertising.
Share your works, get new contacts, redirect them to your gig. 