I would think so. The value of an item is entirely subjective and based on availability, popularity, age, uniqueness, condition, and other such factors. So I would think that an item that consistently sells well over a long period of time is priced right. If it were not, then the value would go down over time. Take the stupid zhu zhu pets from this past christmas. An $8 item was selling on ebay and craigslist for anywhere from $20-$50 because of short supply and high demand. But everyone buying these things knew that the craze would be over after christmas. Sure enough, stores are stocked with them now. I even saw a car sitting on the side of the road with zhu zhu stuff on a table. My guess is leftover stock that they couldn't push before christmas and now they are stuck with them. Fad items start high and then return to a normal selling price.

In contrast, some people pay good money for items I think are worthless. Elvis (or Michael Jackson) memorabilia come to mind. Didn't Michael's rhinestone glove sell for like $350K. To me, it's not worth $5 but someone else thought it was worth $350K. It may turn out that it will be worth more in the future and it was a good investment. Or, it may turn out to be worth less. That's a gamble but investors do it all the time.

But an item that has consistent sales over a long period of time, I would think, shows that the marketplace can handle it just as is. I'm trying to think of an example of something that has been around for a long time and still sells at a similar price (allowing for inflation). I'm not sure if this is a good example but computers come to mind. They are sold in all different price points. However, when we go to buy them, we generally pay about the same price each time because we are often looking for the most up to date computers with good graphic capabilities. So, does this make it a good product, I think so if I consistently go back for the same product because I was happy with it before and think I will be just as happy with an updated version. If I were not happy, I would probably switch manufacturers.

It is worth the price to the people willing to pay for it and want it. That's how markets work. It has been successfully marketed and branded.
There is such a thing as a natural cycle for a product, but that is for another question.

There is also such a thing as cost accounting. That would be another definition

I wouldn't say so. I happen to know the cost of manufacture of quite a few appliances, based on the job that I used to have. The actual value, or worth of the item, in my opinion, is the cost to manufacture. I believe in a fair cost addition to cover profit to merchants, cost of transportation, and cost of inventory warehouse storage, but that is part of our economic system it doesn't really effect the value or cost of manufacture. Being able to sell something for an astronomical profit margin doesn't change the fact of what it cost you to manufacture it.

What is the product and how many have they sold?

Yes, a sustainable price over a long period of time is the correct price by definition, provided that the company does not have a monopoly.

I believe in the free market system. I know that a certain amount of regulation is needed to keep companies honest, but I really believe the market should determine prices based on supply and demand. That way companies don't end up producing a bunch of goods that go to waste, and customers don't have to wait long periods of time so that artificially low production can be adjusted.

These types of things happened in the former Soviet Union all the time. Production was regulated according to how many workers needed how many hours, and that screwed up supply and demand so badly that the economy collapsed.