ANSWER TO THE QUESTION : HOW TO DETECT MAWDOO' HADEETH ?
Firstly, it is when the narrator himself admits that he has fabricated this Hadeeth. For example, Abdul Kareem Ibn Abi Al-'Awjaah said that I have fabricated 4000 Hadeeth.
Secondly, it is when in the Isnaad (chain of narration) of the Hadeeth, there is a narrator whom the scholars of Jarh wat Ta'deel considered as liar. For example, the narrator Sulaymaan Ibn Amr.
Thirdly, it is when we find that a Hadeeth praises a Mazhab (school of thought). For example, the following Hadeeth : Among my Ummah, there will come a man called Abu Hanifa. On the Day of Resurrection, he will be the light of my Ummah....
But, we must know that detecting / searching for mawdou' Hadeeth, it is the work of the Muhadditheen, and not "common people" like us. So, we must always refer to Ulamaa in our Deen.