what can reasonably be expected of a seller?

I would expect this as a seller.
1. Know the condition of the item you are selling. Describe that in detail to the seller. That includes pictures, functionality, known defects, history repair, etc. Don’t say I did not have time to test item, look at it or otherwise. If you have too much to sell, too much to do, you are just a money maker not concerned in any way about a buyer.
2. Be somewhat knowledgeable about the item. A CD player has a drawer, DAC, output connections (rca, optical, balanced, etc) laser and so on. If you cannot answer basic questions about item, you probably should not be selling it. Especially if it is a high-end product and you want substantial cash.
3. Be detailed about how you will pack and ship item. What carriers will you offer? How far will you ship? International? Will you offer to meet halfway to avoid shipping? How well will you package item and do you know how? Many turntables and tube amps will be damaged if the seller just throws item into a box of peanuts. Are you just wanting to ship item, regardless of safety and insure item so that when it shows up in a heap of wires your response will be, “don’t worry just collect insurance money”? No thanks!!
4. Do you offer any returns or refunds and what are the conditions upfront? Do you offer that item will be arrive as it was when shipped or you will offer buyer something if not? Will item be shipped in original box? Double boxed? Once I ordered a subwoofer and it arrived damaged. The seller asked to take detailed picures, sent me a return shipping label and stated he would turn in the claim. He stated he paid to have it professionally packed and he would take it up with them. He apologized to me! That is really above board.
5. Be available and communicative. Many, many deals go south because the seller does not think it is appropriate to be communicating with the buyer. If you are too busy to answer emails in a week, a phone call that goes direct to voicemail or just unanswered I don’t think you will make a good seller.
6. State what you think is the buyers responsibilities. They have a role to play in the transaction that is crucial. If you think the buyer should have 3 days to inspect, install, operate and test item before a return, state that upfront.
7.  Above all else, be honest and fair. I cannot, as a buyer, expect a perfect item, perfect shipping and perfect transaction every time. If something goes wrong in the deal be fair, be honest. Try to save the deal if possible by bending a little.

Very good points 2psyop!

If an item is truly untested for whatever possibly genuine reason then it should be priced accordingly, not within a couple of cents of guaranteed top flight item.

Now wait a second, I can't speak for those second rate carriers but if you mail something through the Post Office, either the sender or addressee can initiate the claim.You can designate which should be the payee. I would always advise customers though, insist on a refund from the seller first. The buyer, if pursuing the claim in hope of recompense, may face a denied claim and be left holding the bag. A seller that says you, the buyer, should file the claim, is dismissing his responsibility and leaving the onus on the buyer. Don't fall for that.The last thing you want is both a broken or lost item and the headache of a claim. Have the seller refund and file the claim.

I did not take the time to read the entire thread.  So, if the following is duplicative of one or more previous posts, I apologize.  Unless I am looking for parts, I don't bother with any "ambiguous" listings as a matter of course - no matter how interested I might be in a particular piece of kit.  If something looks like trouble, odds are it is.  Fortunately, the Audiogon feedback and rating system offers pretty good protection against bad transactions (when coupled with a PayPal facilitated payment).  In sum, if an offering smells a little fishy or looks to good to be true, run, don't walk, away.  My $0.02.

i can tell you of several horror stories i have experienced with shipping issues, sellers and packaging issueswith electronic equipment.
1.  unit was in a high end motorhome that had a fire, units have some smoke damage, but functional... ya right... got both units and when opened up they looked like there was a thermonuclear event contained within the case.. probably what caused the motorhome fire!
2.  such poor packaging that one of the inverter units was hanging half out the corner of the carton/box the main unit was shipped in.
3. my favorite...  a $10k inverter system, well packaged,  i witness the fedex driver show up at my house, walk to the back of the truck, slide open the door, climb in and pitch the box out onto the pavement, clearly about 6ft at the apex of trajectory before slamming down on the asphalt, flat on the bottom.... i was horrified!  and of course chewed the driver up so bad that from then on she would come to my door with packages carefully in hand to personally hand them to me...   thanks to the sellers overly careful packaging, the unit was not damaged and worked just fine.
my thinking now, that i am on fixed income and not making as much as i did back then, if i want to buy something of serious value, i am going to buy a plane ticket is need be to personally inspect and test before i buy it, then i will package it for shipping myself!
bob g