This system seems to be giving a random rate to public keys of those who mined a block in the code you shared above.
My thesis is that the wanted a sort of ebay's stars system, you would gain reputation by mining honest blocks, this reputation would show up in the marketplace. He must have had ideas to try to incentive people into doing transactions in a world where Bitcoin was worth 0, he needed a context, so he was building this web of trust based market. There's a more lines related to the marketplace in 1.0.0 including atom propagation and review functions
https://github.com/trottier/original-bitcoin/blob/master/src/market.cpp
I think this was removed in 0.1.5, this is the last time I found it
https://github.com/blaesus/tinybtc/wiki/Bitcoin-0.1.5-LOC-statistics