I think you're more likely to be knocked down by a forklift than get a kilo of tomatoes!
Having walked past the market almost daily going to work, it appears to be trade-only. The market hall is not at all geared to the public and I've only ever seen things sold by the box, sack or hundredweight. I feel that if you wanted to buy - for example - a box of oranges for football match half time - they might entertain you, but I think you'll be told where to go if you want 200grammes of mushrooms!
Moore St seems to be the closest alternative and is much more user friendly if slightly dearer.