Don't design a machine with sharp edges or garish colors, as this may deter users. Avoid placing the touchscreen, perfume bottle input, or thermal printer in hard-to-reach locations. The machine shouldn't be bulky or contain visible internal parts, detracting from its sleek design. Do not forget to include clear but unobtrusive signage for inputs and outputs. Steer clear of a complicated interface, as it could be off-putting for potential users.