Commodity

When I think of the word commodity I first think of either the phrase "hot commodity" or something that is traded.

A commodity is never cheap or undesirable. It is always an advantage, something that can be used to an advantage, or something that can be traded. In fact it comes from the same root as convenient.

It's a generic word that can be used both positively or negatively.

A Commodity is something you can sell, trade, etc, so it obviously has some value.

The commodity can be something that in small amounts has little value, so tends to be traded in large quantities. This would be generally refered to as a common commodity.

A rare commodity on the other hand, has high value in small amounts.

I think it depends on the product in question. For a soft drink to be a commodity is an appropriate and positive thing; for a lover, musician or some form/genre of artistry to become a commodity is a bad thing.

I've never heard a commodity as something common, cheap, or undesireable. The closest word I can think of to what you are describing is "commonplace." I agree with IngisKahn: "a commodity is never cheap or undesireable."

In alison's example of musicians or art forms, however, I have to say that it IS bad to be a commodity in art, but not due to perceptions of being common or generic. When musicians are called commodities, they are seen as being able to make lots of money for their record labels. This is negative because music is being perceived as a business product to sell, rather than an art form and a form of expression.

From what I´ve heard, a commodity is a good that is sold at a single price everywhere, because its properties are standardized, like refined metals, oil or wheat. Sure you can get different qualities at different prices, but for the most part of the mass production of a commodity, you don´t care who made it because the price and the quality are the same. Also, the seller cannot set the price, as it's determined by the market.
That leads to the usage of "commodity" as something you can found everywhere, being the same as the one you can found anywhere.
For that reason, I think it's a bad thing to be a commodity in music, because it implies that you are "just one more of the heap of people singing the same thing". The reason why those artists usually sell more is beyond me.
For material goods, I don't think it's a good thing or a bad thing to be a commodity. It just implies availability and indistinguishability.

'Commodity' is neutral. The context gives it negative or positive meaning or leaves it neutral.