I've seen repeated comments about not leaving bins to be pushed through by the bags behind yours on the belt.

To me, it makes sense why people do that. It's unlikely that someone will take your items, especially luggage, off of the inbound x-ray belt and walk against the flow of people in the queue. It's much more likely that someone will take your laptop or wallet coming out of the x-ray, claiming it was a simple mistake if they are caught. I've seen this happen: it did appear to be a mistake, but an experienced thief would make it look that way.

Is there any way to guard against this? Especially if the person in front of you alarms, it's not always possible to watch your bags while waiting in the queue. The only way to minimize the risk is to expect that the person behind you will push your bags or bins onto the moving belt. This is especially true when the operator backs the belt up to re-scan a bag.