Regarding people selling equipment to U.S.A. only

You would think so.
I just sold an amp on e-bay to an overseas buyer. When he found it would cost 250 US to ship he backed out and left me stuck.

I have sold a couple of things to overseas buyers. These were just cables and light enexpensive dig. gear (AA) I was never the money; just ther risk of damage and the buyer 1/2 way on the other side of the world. Many things are a risk just going coast to coast. Those I prefer to sell--or buy--- local.

I've bought and sold several things to Cananda, Australia and Japan. Mostly cables, tubes, and asssories. All been pretty straitforward to me. As long as the other person pays in US$ and covers shipping..it's not that big of a deal.

I've sold several things overseas, I'm always upfront with the buyers regarding shipping costs, which can be quite high. I sold an older Mcintosh pre to a guy in Japan who wanted it Express mail, and didn't bat an eye at the $275 US shipping.

Canada seems harder to ship to due to all the additional forms, and EVERYTHING seems to get tied up in customs, but otherwise it's not that bad. I personally will ship anywhere if they will cover the shipping.

Agree that it is the shipping that is a deterrent.
I sold some speaker parts (Infinity EMIM's) to a fellow in Germany. The shipping for those small and light (2 lb.)parts was $90.00 He wasn't bothered by the cost, and I was happy to sell them for what I was asking.
The cost for electronics would be prohibitive. Imagine selling an amp for $1,000 and the shipping (by air) is $700. Very few folks would do it. So why offer to try?
The folks with buckets of money might, but they can buy locally too.
I don't think it is primarily the fear of being ripped off: mostly the shipping expenses. And a return would be unthinkable!! That alone would turn me off! Say you buy the preamp, and ship it and the buyer complains? Geez the return shipping with the original shipping and the buyer could have bought the item NEW, locally.