You are both 'at fault.' You are negligent for not realising what the $5 was for when a reasonable SR user would have realised that 1) it was for tracking 2) regardless, items with an aggregate value of around $200-$250 should be tracked and insured for obvious reasons.

The owner of the razors was careless of his own property by not specifying he wanted insurance and tracking. However, it should be policy on your behalf if this is a service you are providing and you should have made that clear from the start.

Possible solution? You split the costs and either refund a partial value of whatever you both consider it to be provided none of the items had 'sentimental value' in which case god help us(!); or as you already mentioned you donate a couple of razors as compensation.

Sounds fair.

Is there not a possibility that as it has only been 1 week they may still arrive?