Several years ago, my mom ran low on money, so she decided to sell her old wedding ring. She hadn't worn it for years because she and my dad got divorced long ago, so she figured she'd at least get some liquid cash by selling it.
The first shop she took it to offered a little under 10% of what it cost. She thought the shop was trying to scam her, so she went to a bunch of other shops, and they all offered less. So she went back to the first shop a couple of days later, and there was a different guy there who told her that the first guy was an idiot who overvalued the diamond. It was a piece of junk, and it was worth well under 10% of what it cost. The jeweler also pointed out, in detail, that the diamond itself was really shitty even by the standards of wedding rings. But because they already made that offer, they decided to honor it anyway just to avoid any drama. And so my mom sold a ring that cost her and my dad $30k for about $2600.
And I understand that's normal. Retailers mark new diamond rings up like crazy because that's how much people are willing to pay for a wedding ring, even if it's not what the stone is actually worth.