Two sections of the article below are particularly interesting and insightful:

1. „The first time Hellfire Cannon was used was in Aleppo’s Ashrafieh neighborhood, causing severe damage in addition to killing and wounding dozens of civilians. Currently, fighters of the Islamic Front began to target the Citadel of Aleppo with these shells.“

2. „Arms manufacturing plants spread rapidly in Aleppo and its countryside and manufacturers found a large market to sell their products. It is believed that the Islamic State in Iraq and Syria (ISIS) took advantage of its presence in Aleppo and its nearby countryside to persuade plant owners affiliated with the Free Syrian Army to manufacture hundreds of Hell Cannon bombs for double the price. Some of them moved to al-Bab and Manbij after ISIS was expelled from Aleppo. “

http://english.al-akhbar.com/content/after-%E2%80%98hellfire%E2%80%99-and-%E2%80%98hell%E2%80%99-meet-syrian-rebels%E2%80%99-new-rocket-aleppo

Here another article about rebels using gas canisters as weapon against civilian areas (of course western press does not consider pro-government civilians as „real civilians“):
http://www.dailystar.com.lb/News/Middle-East/2014/Nov-30/279371-rebel-fire-kills-mother-3-sons-in-syrias-aleppo-monitor.ashx

So, the rebels do not only indiscriminately shell civilian areas, they also produce arms and sell them to ISIS.
So much about differentiating between ISIS and „good“ rebels.