When all you ever do everytime you use your social networking account is sell your products or promote your business, chances are your contacts will no longer pay attention to your posts.
While for social gatherings there are appropriate social graces, rules for social networking are now being established. Here's one rule that is appropriate for all the major social networking sites such as Facebook, Twitter and LinkedIn. Communicate with your customers and friends - speak TO them and not AT them.
Social networking sites require interaction and your goal when signing up for these sites is to get to know people better or have conversation with your friends. The line that separates selling and keeping your online relationship with your contacts is very thin so you have to make sure that you examine your posts well.
A post that goes like this "So many people are visiting the new museum in town, I feel like asking if I can exhibit my pieces there." would surely solicit comments and suggestions. This is definitely better than saying "Beautiful art pieces for sale."
Are your posts maintaining relationships and helping your business at the same time?