you have to assume the amp works. this will happen for commercially purchased amps, so long as you use a speaker or combination of speakers such that the load is equal to or greater then the minimum listed. eg, if the amp is 4ohm stable, then you need a 4ohm load or more. a 2ohm load would be "unsafe".
the DMM only gets you close to the point of clipping. not that it matters. if the amp has an unregulated PSU, the the point of clipping will change based upon the battery voltage. it won't really matter too much. thus there is arguably little point in actually using an oscope unless you are competing.
and of course, there is no reason to use this maximum setting. things may sound better at lower settings. especailly if the speakers are distressed at this optimum power output. the DMM/Oscope provide a safety mechanism, but give no info on how things will sound.