I was actually thinking about this recently. I'm not sure if a marketplace like this already exists, but I'd like a site where you could only list domains for a max price of say $200.
So many domainers price themselves out of the market, and perhaps having such a sales platform might encourage liquidity on the back of more realistic prices. It would just probably end up domainers selling to other domainers, but I have plenty of names I'd sell for less than $200 to keep the bank account ticking over, and in addition to that, I would enjoy browsing those listings for bargains.