Following are the factors that should govern your considerations when comparing used dehumidifiers.
Capacity: Humidity removal capacity determines the amount of moisture that the unit can effectively remove from the surrounding atmosphere in a single day. The crucial factor here lies with the environment for which you want to implement the unit, for example your residential building, industrial settlement, storage units, food processing plants, basement, etc. A large area is prone to higher humidity levels, thereby compelling the need of a large capacity unit.
Energy efficiency: Systems that are designed to operate under heavy-duty conditions, such as large industrial or commercial settings, are obviously to consume a bigger load of power, which can result in skyrocketing electricity bills. Hence, check for features that aid in energy efficiency and help reduce excess power consumption, such as adjustable humidity controls, efficient compressor, delay timer, automatic shut down, dual operation - ventilation and dehumidification, etc.
Noise level: Operational noise depends on device to device, and is strongly dependent on the environment that you are looking to implement the unit in. For large areas, a machine with an adequate noise level can still be considered, in contrasted to residential areas such as bedrooms or halls, where silent operation is of prime importance.
Pricing: The more the unit is packed with robust features, the higher the price chart will rise. Therefore, it depends upon your selection of used dehumidifiers that aligns with your humidity moderation needs.