I usually ship between 40-50 coins a month, with $300 being about the average price. I think I might have 1 or 2 coins get lost a year on average. I would have to lose a coin every month and a half or so to make buying insurance worth the cost.
That reminds me of a time I bought an item on ebay 3 years ago (low value item, only $50). It scans "sorted and out for delivery" on USPS tracking 250 miles north of my town and in obviously a completely different zip code. There wasn't even a street name in that city that matched my street, to make it funnier (I used google maps to see if I could actually FIND an identical street name there, no luck). What could possibly mess up a delivery THAT MUCH??? After a couple of emails they admitted the mistake, package went back to one of the main sort facilities and came down here next day. It was an area I've never had a previous address even near, so I know 100% it wasn't the sellers fault for it ending up so far away. And the label was printed, no less. Are they hiring people who both cannot read and speak English?
I had 2 lost packages last year. One for $51 and one for $734. That one about killed me, because 2015 was my worst business year for coins since I started doing this and quit my career.
If you are shipping with any significant value frequently, look into an insurance policy that covers shipping, rather than buying insurance for each package. I have a policy from Hugh Wood that not only covers shipping, but also stuff currently in my possession, and in my SDB, from the time I pick it up from the post office to the time I drop it off again. It's hard to describe a single solution for everyone with regard to insurance, but you owe it to yourself to look at the different types of coverage available and determine which is best for your situation, including self-insuring up to some threshold of pain that only you can determine.
That's my use case - not counting commissioned sales, I haven't sold 1000 units of my own over the past 17 years, and my offerings are usually in the $50-250 range where I really wouldn't care to suck up the cost on my own. That said, I've only had one package go missing in that time, and it ended up a case which (among many other disappearances) was prosecuted against a US Mail employee. I like to think the insurance - manifesting Murphy's Law - is responsible for that record of safety.
I have not had to file a claim, but on several occasions I have reprinted on the various forums the sections from the Domestic Mailing Manual that clearly indicate that they DO cover the numismatic value on coins, and the PM's are only covered (for more then $15) if they are sent by Registered mail. I also posted the sections that indicated how you can establish the value for numismatic coins in the case of a claim. I don't know about "international Registered mail" but on regular Registered mail shipped outside the country, it is covered for the full declared amount UNTIL it leaves the country. After it leaves the country, the Postal Services maximum reimbursement if lost is $49.
FWIW, I did get an insurance re-imbursement on a ~$700 rare stamp set earlier this year. It was going overseas, I used ShipCover. It took 8 weeks to process, and I was on pins and needles. I did get all my money back - excluding shipping and insurance costs. If you get insurance, always follow every letter of the rules. Even then, their objective is NOT to pay you - so sometimes you need to step up and be persistent. File claims immediately, get confirmation, get confirmation AGAIN, ask about the timeline, and don't let a day go by outside the timeline. Don't harass the person on the phone, they *can* help you. Make them your friend. If you annoy them, they won't lift a finger - and may even recommend not fulfilling the claim if they can find a way. There is no hard and fast rule for insurance. What are you shipping? Where is it going? How well is it packaged? What is the reputation of the buyer? How much can you afford to lose?
I ship 50+ packages a month ranging from a few dollars to a few thousand and in the last 2yrs I've only had 1 recipient say they didn't get they're package (knock on wood) but that was because the buyer gave me a previous address and the current occupant was, as he put it, a "nasty old bastard" that said he "never got nothin" but the buyer was convinced the guy lied to him since the tracking said it was delivered to that address. I offered to refund him, something like $200, to keep his business but he wouldn't hear of it as it was his fault. I was sure he'd say that but it's just good business to offer imo. I usually only pay for insurance if it's over $400 and go registered over around $1000-1500 depending on how far it's going