Buyers should prioritize the Pressure Rating (PSI) and Water Flow Rate (GPM). For commercial use, a minimum of 3000 PSI and 4.0 GPM is recommended to ensure efficiency. Additionally, verify the Engine Type (e.g., Honda or Loncin for gasoline units) and the Pump Quality (Triplex plunger pumps are preferred for their longevity compared to axial pumps). If the unit is a self-contained vehicle, check the Water Tank Capacity (typically 200L to 1000L) and the Material (High-density polyethylene or stainless steel) to prevent corrosion.