Well Sony MRP prices are made in such a way that they work throughout india and the best street prices with bill and warranty are not much different from MRP price.
Since Sony lcd are a direct import they attract a duty of around 35% ,compared that to samsung and lg which are assembled in india and perhaps some components like power supply,bezel are made in india by local oem,only the lcd panel is directly imported which attracts a duty of just 5%.
So in the grey market they by pass the 35% duties which make it a really tempting deal.Grey dealers rarely sell brand like lg or samsung since there is not much of a margin.