I don't think any of that is true.

There are many people who have a social dislike for haggling for anything.

There are many places that offer used merchandise for a fixed price that people shop at, flea markets are fairly unsuccessful in the market for used merchandise. There are many stores that sell jewelry at a fixed price. Stories about people groaning about bidding wars on homes are ubiquitous. And some sellers don't negotiate.

Consumers are consumers, and some cross-section of them will always lack negotiation skills and/or have a distaste for the practice.