Crime festivals like Harrogate succeed or fail to a large extent through the quality of their panels and main events. But of course, quality is not entirely dependent on the fame of the panellists (and thank goodness for that!) Much depends on how the different people involved gell together.
I did feel that our 'legal eagles' panel was one where the different personalities clicked together. A good moderator like Peter McCormick helps. Another example was a panel called 'What Lies Beneath', on psychological crime fiction. The moderator was N.J. Cooper, a fine writer who is also supremely accomplished at putting people at their ease and creating a feelgood factor.
A different situation occurred when the moderator of a conversation between the American thriller writers Linwood Barclay and Lisa Gardner clearly found the task of public speaking a bit of a challenge. A tricky situation that anyone can sympathise with - it took me years to feel comfortable with speaking in public, so my heart went out to the person involved - and one that was happily redeemed by the evident good chemistry between the two authors. I've never read a Linwood Barclay book, but his wit and genial manner made me interested in his work.
Which leads me to another point. You can like a person and not necessarily like their books. But it's true, I think, that if one comes across a previously unfamiliar author at a convention and finds them personally appealing, one is more tempted to read their books. It may not be logical, but I think it happens a lot.