Looking at the outlet in the top left corner, you will see a white wire that is looping to the green screw at the bottom. This is referred to as a false-ground or bootleg, in my real-estate world not-so honest sellers (sometimes known as flippers) have called this looping. The purpose of this technique is to give the appearance that the home has updated wiring and is safe. Depending on the not-so honest seller, they may hide the wiring in a junction box in the wall out of site where the old wire meets the new wire. It usually takes a Thermal Imager to find this box.(Yes I own one of these to).
This connection may make it appear that the circuit is "grounded" since a test that connects the hot side of the receptacle to the ground port will show current flowing, but this is incorrect.
Not only does a "false ground" electrical receptacle lack an actual safe alternative path to earth through a separate ground path or grounding conductor, but worse, the "ground" connection, by being wired to the neutral side of the circuit, can cause dangerous electrical shock as well as damage to equipment plugged into such an electrical outlet. The picture to the right is a simple $7 tester that tests this outlet as OK. Two green lights means the outlet is ok. The inspector that uses the not so advance equipment, is a not-so honest sellers dream. The Ideal tester I use clearly shows False Ground on the display, or the Inspector 2 shows a little yellow light that tells me something is wrong with the ground wire. (Bottom 2 pictures)
Sometimes it is just a home owner trying to save money by doing the work themselves or hiring uncle Bob and both figuring out the cheapest way to get the job done. Eitherway whether Mr. Flipper or Uncle Bob you"DESERVE" a Master Home Inspector with the right tools. So that their cheapness does not become your expense.
This is just one example of things sellers, whether intentional or not do, that later can cost you money.