Top-left panel: Example of high-z candidate selected based on the initial optical/IR selections from DES and catWISE, but then discarded after a visual inspection of its g-band image. We note that the image has been smoothed with a Gaussian filter in order to make the faint signals at the position of the optical source more evident. Top-right panel: Example of a selected candidate which was then discarded based on the NIR photometric points (from VHS). The black solid line is a template for high-z quasars and the red solid line is a template for an elliptical galaxy. In this specific case, the source is likely an elliptical galaxy at z ∼ 1.1. Bottom-left panel: Example of the LBT/MODS spectrum of a candidate (RACS J1521−00) not confirmed to be at high redshift. In this specific case, the target is likely a type M brown dwarf. The grey spectrum is at a resolution of ∼0.9 Å, whereas the black one is binned at ∼3.5 Å. Bottom-right panel: ATCA image at 5.5 GHz of RACS J0622−51, a candidate selected based on its optical/NIR colours and a radio association in the RACS-low survey within 3″ (dashed circle). The black cross shows the optical position of the high-z candidate. The radio source detected with the ATCA revealed the RACS-low association to be spurious, with the radio source being > 10σ away from the optical counterpart, with σ = 0.24″ the uncertainty on the ATCA position derived from the fit of the radio source. The black contours in the image are drawn at -3, 3, 3$\sqrt{2}$, 6 times the RMS of the image (RMS = 27 μ Jy beam⁻¹).