Im so glad you went here! Its amazing isn't it, utterly manic. He still uses a massive Record Price Guide book to price everything as well.
I have mentioned this before, but to the right of your photo you might have seen hints of another space? There is a staircase around the corner that leads to another room upstairs. Supposedly this is where the rare stuff is kept and is arranged neatly.....not sure when the last time anyone was actually able to get there was though!
Edit: Found a photo I took when I was there with the blocked up corridor to the left.
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