It's a few years now since i made the trip, trains being a real pain on a Sunday. However I might just make the effort this year.
The last time I went I made the mistake of purchasing a rather expensive vintage pen from a stall located on the corner where the floor plan shows 24 (probably not that exact table). The lighting was not great and it was only after I was on the train home that I spotted a significant hairline. I suspect the seller was very aware of the issue and making the most of the circumstances.
Taking a loupe or avoiding darker corners would be my advice to those wanting value for money.