Social networks have millions of visitors every dingle day. This is an advantage for webmasters, because they can use those websites to bring traffic to their sites.
Since social networks are free to join and they help people to communicate, most of internet users have an account with them. So is the best place to find many people together and promote them your products.
The key to have success with this method is not spamming. There is not need of posting the same thing more than once a day, better post it once every 3 days and try to change something about it each time (add a similar title, change a few things on the description etc)
Also do not post direct link to the page of the purchase. Better drive your visitors on a page where there will be a full description, reviews and images of what you are selling.
Hope my recommendations are helpful for everyone. Do you have any tips to share?