He technically didn't pass out bad information, however he should've put your son into a correct arrow spine per his bow config and measurements.

Depending on the arrow your son picked, a longer arrow would be proper due to the arrows spine. IF cut the arrows spine could have been too stiff for the bow, however if that were the case, the shop worker should have recommended a fix like the properly spined arrow at the correct length optimizing the bows performance.

Sounds like a lazy shop worker unless your son was adamant about the arrow he selected.

<font color=blue>Good Luck and Good Shooting</font id=blue>

<font color=red>Rob</font id=red>