I honestly think that sending a high value small item through the post is high risk due to fraud by almost anyone involved in the process. Watches are well sought after by rouges and villains.
Even weighing the parcel at every stage of the process is not that useful because the famous pebble in the box still weighs the same.
If you cannot buy it locally or are prepared to travel to do a deal, just forget it. No watch is worth the worry.