A dtg printer will use electronic pulses to control either a belt or screw drive to move the platen or printer. Both options are viable means for moving the necessary item (i.e. the platen or the printer). If the dtg printer uses a belt drive, make sure that the belt is pre-stretched or has a teflon coating on it minimize any stretching that will typically occur to a belt drive over time.
Brother GT-541 Belt Drive
If it uses a screw driver, make sure you ask whether there is any maintenance or lubrication need to be done to it.
Flexi-Jet Screw Drive
Whether the dtg printer has the platen move under the print head or the printer moves over a stationary platen, it uses rails to keep the moving part aligned with the stationary part in a similar fashion of how trains run on railroad tracks. These rails can either be a draw slider type or a solid shaft using a linear bearing system. A draw slider type rail has channels that the part slides forward and back like a kitchen cabinet drawer.
T-Jet3 Slide Rails
A solid shaft / linear bearing system transfers the majority of the weight to the bearings and puts less stress on the motor that drives the movable part.
GT-541 Solid Linear Rails
MAINTENANCE WARNING: Some dtg printers require you to keep the rails lubricated. Contact your manufacturer to determine what maintenance, if any, is necessary for the rails.