Hi.  Looked at a job that has sporadic sunken tiles.  I didn't notice much of the kind of lippage where the tiles are uneven all around, but there are tiles here and there where one corner has sunk down below the level of the ones around it.  I don't think grinding would help much, but there could be a lot of hand polishing in those corners to get picture framing out if there is not another solution.  Does anyone have much experience with this situation?