oh well shit always happens. Any equipment can fail, unfortunately. And it may also depend on the single unit, some may have bad luck while some otherm ay not, and also on the way they're used/abused or mistreated.
Oh yes! Great buying used. Every multiFX I know of, can be factory-reset
They are circuits, they either work or they don't at all.
Guitar are much riskier to be used, IMO...