Because my shop facebook account is linked to twitter, anything I post goes through which is good because I post other things besides my items on my FB page -- I do a happy birthday to artists born that day including images, suggest websites and articles, salute shops I like, mention music playing that day. Since I don't list a lot of items at a time, 1-2 and I sometimes only list every other day. This way, people aren't overwhelmed with my listings.
One thing I am very annoyed by, though, are the many people who retweet, retweet, retweet. Someone told me that it was good etiquette to RT everyone who follows you. Maybe. But I don't. I retweet sparingly. Otherwise, it seems mindless, lacking consideration and actual interest in what is being retweeted.
I'm also not fond of all the people who post inspirational quotes as if they had nothing else to post about.
I read a lot of blogs about social media and one thing they repeat over and over -- content, content, content. If all your tweets (or FB posts or any other social media posts) are quotes, shop listings, retweets of other shop listings, or endless updates on where you are and what you're doing, then no one will want to follow you.
So I strive to make my content at least remotely interesting and I am getting response to my artist birthday series, to the occasional funny cartoon I post, the occasional art inspiration piece, and even my own listings. It takes work and dedication to do it right and I think I finally hit on the right combo.