I have no induction cooker available for inspection, reviewing user manuals it seems to me that at least international manufacturers like Philips provide appropriate shielding. This can be either a ferrite plate below the induction coil or a massive conductive shield at the appliance bottom.
The problem is however that these shielding means 1. cause extra manufacturing costs and 2. involve some unwanted losses. So if you can be sure that there's sufficient space free of conductive or magnetic material below the induction coil, using no shielding at all is the cheaper and more efficient alternative.