Anything can be developed. Even Herbsmarkets.com (which is available and has the same GD appraisal value as yours) can also be developed and made to come to the first page of Google with good optimization. But to sell a domain without any website you need to ask yourself if this holds any commercial value if it sounds right. HerbMarket and HerbsMarket make more sense to the buyer. While purchasing a name, try to ignore plurals if the singular word is making more sense.
My appraisal: $250 - $750
It really depends on the name. Markets – its something from financial news or economic analysis. Like "markets are improving". Who would name a company "[...]markets"? The same with "[...]shops", "[...]stores", "[...]banks".
There is a difference between being a seller - market and being an intermediary or just a hub for other markets.
Plural isn't always useless, but it can drastically change the expected outcome of a website.