Quiet
In the few sales that I've completed on the exchange as the seller, I've always shipped with signature confirmation upon delivery (and insurance and tracking). It's something that I didn't hide or spring on the buyer though; I list it as being something included in the price of the knife upon purchase in my sales threads. If someone who was interested in buying a knife that I was selling request that it not be purchased with shipping, I likely would cater to the request (the caveat here being that the knives I have sold and that are in my collection to sell are not extremely valuable - they're just standard models of production folders from companies like Benchmade or Spyderco). You're selling to somone and in my opinion
you should want them to be satisfied with the experience of dealing with you as well as what they are getting.
Having said that, in my (relatively few) purchases off the Canadian exchange (I reside in Canada), I have twice had packages go "missing" via Canada Post. In both cases, it ended up being (what I like to think was an) honest mistake; the package intending to be delivered to my residence with the home address "X885" was instead delivered to "X855" just down the street. I'll also add that rather than mail being delivered personally to each home in my neighbourhood, there is a community mailbox with locked boxes for each house and a few oversixed boxes which the courier has the keys to which they can leave in your personal box if the item being delivered won't fit in it. Given this system, it's likely that in their haste to deliver the mail, they simply put my knives in the wrong box - a much easier mistake to make than physically walking all the way up to the wrong house (or so I'd like to think).
In both cases, the sender hadn't opted for signature confirmation upon delivery so even though the packages were being shown as "delivered" they were nowhere to be found for myself. The first time this occurred, there was a little more wondering as to where the package was by both myself and the seller. The second time around, given my prior experience, I rightly figured that it was just a repeat of the case of the first "missing" package. Luckily, I have a friendly and conscientious neighbour (plenty actually) and got both knives a few days after they were "delivered".
The reason for the short story is this: in both of those cases, particularly the second time around, I didn't immediately jump to the conclusion of being scammed or that the knife was stolen in transit. However, until my neighbour was able to link up with me and deliver the packages, I couldn't rule out either of those scenarios as being the reality (although I had serious doubts about the scamming scenario given my previous dialogue with both sellers). One of the major benefits in my opinion of signature confirmation is that until the courier can physically get someone to sign for and take possession of the item(s) in question, it remains in the possession of the Postal Service which in turn also means that if it's not delivered to my address, I should be able to expect the package to be at the local post office (as per the delivery slip) where in order to retreive it, I need to be able to prove my place of residence/identity. This provides myself at least with the peace of mind that while I may not be able to have my knife in hand right away, I can be confident on where it is in the meantime. Since knives generally aren't a necessity for my day to day life, I'm willing to accept this trade off. It also doesn't hurt that I live less than a 10 minute drive from the post office.
I'm not disagreeing with you that this can be annoying at times for the buyer (perhaps an understatment?), especially as you have already mentioned that not everyone works regular shifts and/or hours - myself included. However, I feel that for certain buyers and sellers, the extra piece of mind it provides can be worth the potential hassle it may provide.
I haven't amassed a lot of sales here, but like I've said, the few knives I have sold here I mailed with signature confirmation (as was plainly stated in the for sale thread) and I have yet to have someone ask me about not purchasing that option when mailing. Not trying to say everyone has to or should use it though. Just my $0.02 from my (limited) personal experience.
Edited for clarity.