Being an expert in something does not guarantee you are correct about a particular theory. It may lend weight or probability to the statement made.
In the case of a historical Jesus, it is suggested that this theory is accepted without reservation by a number of biblical scholars. This can give us comfort that the theory is correct, but is not definitive. I would still want to see how they came to this view (what is the evidence). Are these scholars biased (ex. were most faithful Christians to begin with?). What do they know about the quality of evidence? As a lawyer I might have different ideas about the admissibility of certain types of evidence (ex. the unreliability of hearsay evidence).
In the case of Socrates, I would think the evidence for his historical existence is better by a few degrees, then the evidence for Jesus. We have first-hand accounts of Socrates, made during his life. I have not studied either question in much detail, and I would be happy to be corrected on either point.
http://freethoughtpedia.com/wiki/Socrates_vs_Jesus