Ghosting can be typically recognized by several waves that follow after a sharp edge of a model. An example can be seen in the photograph of 3DBenchy at the marked spot.
How to fix ghosting:
Adjust belt tension on X and/or Y axes. It may take a bit of time to find the perfect belt tension. We can offer the following tip: try plucking the belt like a guitar string. You should hear a deep bass tone. A belt that has been tightened more will emit a higher tone. A less tightened belt will result in a lower tone.
You can also check the Belt Status values which can be found in the printer’s LCD menu. Go to Support -> Belt Status and check the measured values. Values 240 +/- 40 are fine. These values are updated each time you run the Selftest (LCD menu -> Calibration -> Selftest). A lower value means more belt tension, a higher value means looser belt.
The problem of ghosting can be visible also when belts are properly tightened. Ghosting is caused by vibrations that increase with print speed. To reduce ghosting, try to reduce the printing speed and see if the problem goes away. It’s always better to place the printer on a firm surface.