Why would anyone trust Turkey?

It is not in Turkey's interest to assist the US. Turkey is the land-bridge between Asia and Europe. Turkey has to remain friendly to nearly every nation in the region to maintain their current status. Turkey does not want to alienate themselves from the Middle Eastern Islamic nations and is still trying to acquire admittance into the European Union. Tough stance to play on the fence for so long. The government is being run by the AKP and Edrogan, which is known for their Islamist leanings. In my time in Turkey, I observed many things that make an American cringe, simply because of the stance that Turkey takes toward all foreign nations. Reporting that Turkish Intelligence would sell out a group of US trained elements is not at all surprising or out of the question.

You can understand Turkey's stance by briefly studying Turkish history. Reminiscing their Ottoman Caliphate, many Turks (not all, of course) feel Islamic politics could use a stronger Sunni presence. What we classify as atrocities committed by ISIS is merely a reflection of what the Ottoman Turks have done in their campaigns. Most Turks are nationalists, obsessed with their historic empires (from the Gokturk Khaganate to the Ottoman Empire), ISIS is the excuse some radical Turks have been looking for.

Is Turkey providing more support in the fight against Daesh than Saudi Arabia who, depending on who you ask, spends a little more or a little less than Russia on defense?