While studying the method of images for an infinite grounded plate, I came upon two assumption I can't seem to find the logic for:
The test charge doesn't induce a charge density on the plate which makes the potential anisotropic in space. In other words, the charge doesn't induce a constant charge density (or any other such charge density) on the plate that makes potential at infinity different for different directions.
The grounded plate is a conductor, and hence for each induced negative charge, there should be an equal positive charge residing somewhere on the plate. But the charge distribution derived using this method doesn't have any positive charge density. [Here, I am assuming that the plate doesn't have to be grounded by any special means - since it extends to infinity (where $V=0$), and being a conductor it is equipotential, hence all points on the plate are automatically at zero potential.]