Tiling grades

I have seen some 300 x 600 rectified ceramic wall tile at a salvage yard. It was labelled as general grade and the sales guy said this meant the glazing over the tile was not up to the standard required to be a premium tile, and there would be tiny gaps in the the glaze over the tile. Despite this, he said he had never heard of anyone having trouble with these tiles, and that the gaps in the glazing would be minor. I am wondering if in the long term these tiles are likely to become porous (we would put them in a bathroom) and whether anyone else has used 'general grade' tiles in thier bathroom with any issues. They are plain white rectangular tiles and very cheap but I don't want to buy something we have to rip of the walls later.