If there's fraud, the airline could cancel at any time. You could even be on the plane if they discover it before take off. If the fraud is discovered before your return trip, then you will be stranded.

What this sounds like is an airline employee using his cheap standby flight privileges (otherwise they'd need your full name etc. well in advance). If that's the case, then you are not guaranteed a place in either direction since it's standby, although the employee will be able to make a good assessment of the likelihood of space being available. If there are IRROPS, then you will be SOL. Obviously what the employee is doing this it's strictly against the terms of his/her contract and will be sacked, if discovered.

The fact you don't want an opinion on the matter speaks volumes.