Premier Colin Barnett is not convinced the merger between BHP Billiton and Rio Tinto's WA iron ore assets is in the best interests of the state, saying the miners could be seeking to avoid paying land taxes.

Premier Colin Barnett is not convinced the merger between BHP Billiton and Rio Tinto's WA iron ore assets is in the best interests of the state, saying the miners could be seeking to avoid paying land taxes.