Everyone gets the occasional rig, however careful one's banding technique.
Most marts have a cut-off date, after which entire male sheep (which would include rigs) cannot be present when breeding females will be present. And some marts like you to separate rams and wethers when selling in the store ring, so that buyers know whether they're getting, or may be getting, animals with testicles or not.
If they're going in the fat ring and are ready now, you're probably safe enough - but if in doubt, check with the mart.