Anything that plugs into a wall has to have safety information on the back panel. If the unit has, for example, a multiple primary transformer that can accommodate different voltages, then all those voltages will be printed and clearly visible. Usually it's in the form of a list with blank boxes and the unit voltage has a mark on the corresponding box. This is the only way to be sure it's convertible without reconfiguring.
If a tech claims to have experience converting operating voltages on that particular unit -- and the unit only has one voltage printed on the back -- you'll have to use your judgment.