Repeating this here in addition to having reported it because I am not 100% sure: since "in foro" takes the ablative case, shouldn't "on the market" also be a correct translation or is that too abstract?
'on the market', in the sense of being available for sale, is not a meaning conveyed by in foro.
I think that 'the book is for sale' could be liber venum datur, but I'm not 100% sure. It is a pretty rare expression to find in classical texts.
A person is "at" the market, never "in", but what about objects? I am more struggling with my understanding of English here than with that of Latin :D
If the book is lying on the ground, I guess 'the book is in the market' would be correct.
Otherwise, think in/at the forum. A Roman Forum was not only a market, but also a place for public gatherings, debates, judicial and religious events, etc.
isn't 'market' kind of a reductive translation of 'forum'? going eng -> lat i can't think of a better translation off the top of my head but from lat -> eng, wouldn't you prefer 'forum'?