Sales indicate how the market views a product, as people vote with their dollars

No, if it was GTA4 and GeOW would have sold no copies while Metroid Prime 3 would have sold a gazillion copies

If sales were an indicator of quality, Blizzard would rule the world. now they are just having games with massive legs :(

Here is what I mean with my real estate example:

Uncharted 2 is a fantastic game.

If you were to rely on an incomplete equasion like sales = quality, you would say that, for instance, Halo 3 is better than Uncharted 2. It might not necessarily be true.

To help determine the quality of a game, by using sales as a factor, you need to use sales relatively.

Uncharted 2 vs Another adventure game exclusive to the PS3 with similar marketing. Preferably a sequel released around the same time on the console.

The only game that comes close to fitting that bill is MGS4, however even then, it is not a valid comparison.

In that instance, sales are not a valid indicator of quality, because you don't have a control game to compare it to.

However, a game like Modern Warfare 2 can be compared to similar games, such as CoD:WaW. If MW2 vastly outsells WaW, then those sales could be used as ONE factor in determining the quality of a game, if your opinion was inclined to do so.

Afterall, we vote for our favorite games with sales. Reviews are only opinion, and all too often, incomplete opinions from people the game was not designed to appeal to.

So absolutely, sales can be used as a factor in one's opinion of quality, and it's very valid, but it is difficult to use that information correctly, and attempts to oversimplify the equation will result in incorrect analysis.

This is the exact same method used to determine the relative value of houses, except the "sales" factor is actually the "prices of similar homes in the neighborhood that have sold recently" factor. The only difference is that it is much more imporant in real-estate apprasial, than it is in the formation of one man's opinion about a videogame's quality.

Hell no.

I think quality is a term only the individual can define, so no. Sales do not = quality, however, they should be taken into consideration since, obviously, a certain number of people decided the game was quality enough to buy.

Honestly people can't agree about what quality means. So how can we say sales are an indicator of 'quality' when that concept itself isn't defined?

If quality means 'am I likely to have fun with this game' then probably yes if applied over a group of individuals.

If quality means 'how does this game rank against another based on some personal notions about what the game should play like' then probably not.

the quantity of sales are a quality of a game.

the preconceived ideas about the 'quality' of the game are a quality of a game (franchises)

Etc.

Nope

The only indicator of quality I believe in is inside my head.

This.

Unless someone considers best mainstream appeal as quality.