Missing shipment

That’s why USPS is only good for insured or certified mail. I’m sorry to say you’re probably SOL. The burden of proof will likely be on you, but try contacting your local postmaster. Who knows..maybe they have an employee who they’ve been suspecting of theft. It happens in that organization.

All someone has to do is wait to see if you're home and then walk up and take the package. Happens all the time in the land of the free. Like stated, unless you're required to sign for it, there's not much you can do.

Check with you neighbors to see if they saw something or someone suspicious loitering about and if they themselves had any problems recently. Police will tell you it's very likely someone who lives close by (within a two block radius) so you might be one of many who've been burgled lately. 

If you're lucky, the idiot will strike again and be caught and hopefully, you and anyone else can inquire and look to see if he has your gear.

All the best,
Nonoise

If an item is insured for at least $200 with USPS, then it will automatically require a signature.

"We did not discuss insurance. I assumed that he would do so since $860 is a significant sum."

Even if the other person was a good friend, I would never assume anything. These days it's best to make sure every "i" is dotted and every "t" is crossed.

I would never have something delivered when no one was home. Ship to work or have it held at the shipper for pick up.

OP - I have made purchases or had equipment delivered without insurance and have never had trouble.  I would go ahead with the "missing mail" report.  I would find out from the seller the size and appearance of the package.  I have heard of people having success doing this and sincerely hope you will be one of them!

Alll the best!

PS  Check with the seller to be sure he had your address information exactly right.  That's a big deal.  If he did possibly mess up you could include the information about the possible mailing mistake to the PO to help the USPS hunt down your package.

I had this happen to me several years back and thought the package was stolen.
Turns out that USPS delivered the package to the wrong address, about 5 houses down the street. I forget how long it took, but it was several days until I got my package.