Market value is subjective; Jack Wighton accepted lesser offer despite bigger ones from others.
Market value is whatever someone is willing to pay.
When Jack Wighton went to South Sydney on a cut-price deal, the justification coming out of the NRL was market value was whatever Wighton was willing to accept.
Never mind that he'd knocked back far bigger offers from not only the Canberra Raiders, but the Redcliffe Dolphins as well, before opting to join the Rabbitohs.