73easting, I'm gonna disagree with your observation in that the problems/issues you mention are not unique to gun buyers. This happens with every product sold, not just guns.
I'm not familiar with knitting needles, but
I buy a lot of coins for my collection and tools and you have the exact same thing. There are a number of reasons for this, one of which is...you don't have to face the person your dealing with. It's a lot easier to slam someone via email, feedback, phone or mail than it is to do it in person.
Other reasons...
1. buyers remorse (wife just found out you spend 'her' money).
2. Found the same item cheaper someplace else.
The bitching is caused by both the buyers and sellers. The sellers don't accurately describe what they are selling, and the buyers either don't ask for clarification or have to high an expectation.
The final 'problem' is that many people end up spending more on the auction sites for items they could get other places for less money. They get caught up in the auction. My general rule is that if I can get the item on auction for 20% less than other sources, its a good deal. But many people are trying to get the deals at a 90% discount.
As for the refunding of shipping costs, it depends. If the description was inaccurate, then the seller should refund all costs. If the buyer changes his mind for any reason, then the buyer pays all costs.
Regarding the 'I am going to get screwed" syndrome, unfortunately it's true, but that is because it happens all too often.