I am slightly confused about this topic, why do people muhaditheen differ in grading certain ahadith? Some may grade one as daef and another scholar as sahih. If we know the conditions and have the biographies of the people in the chain then why are there differences? And as most of us are not muhaditheen so how does a student of knowledge go about in differentiating between such ahadith?

The reasons for their differences can be summarized in the following points:

1. Disagreements about narrators. Are they reliable or not?
2. Knowledge of supporting narrations and using them to support a weak narration. Scholars who only have access to one narration will declare it weak and the others will say it’s acceptable.
3. Difference about the conditions set for grading a hadeeth as authentic or not authentic.
4. Knowledge of the science of hadeeth; a scholar who is more proficient and more knowledgeable in the science of hadeeth will give sound judgments about hadeeths which may differ to the judgments given by less proficient scholars.

These are the main reasons. As for what a student of knowledge does when confronted with these differences; the student who is a beginner in the science of hadeeth or does not have the required proficiency to make a judgement has to ask his or her Sheikh and follow his judgement or verdict about that hadeeth. A student could also use the judgements which Sheikh al-Albani gave on hadeeths in his various books. In this case a student is doing taqleed, that is following a scholar of hadeeth because he or she cannot pass judgement on a hadeeth. Later on when a student gains a better understanding of the hadeeth studies, he or she can have a critical approach where he or she examines all the sayings of different scholars concerning a particular hadeeth, weighs them and chooses the strongest opinion according to the rules set down by the scholars of hadeeth.

And Allah knows best.