Don't take it as an offense, because you did truly get very lucky! You really need a shock cushion when shipping lenses, and the best way is to double box the item.
These guys were just pointing out a common mistake in order that you might not have trouble in the future. At the very least, so others would not think your packing job was the proper way to do it!
Double walled cardboard does nothing to protect the lens, because in the event of a direct hit, there is no cushion to absorb the blow! Only double boxing will prevent it, and even then, it doesn't always work! These freight handlers are merciless!


Everything Cities Service
Specializing in old Gas Pumps
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