You check by doing research. I've had a few ideas I thought were gems, then after some research I found a small number of companies doing similar things. This i

You check by doing research. I've had a few ideas I thought were gems, then after some research I found a small number of companies doing similar things. This in itself is not a bad thing. If no one else is doing this ask yourself why? Is it because there is no money/profits in it? Or is it truly a unique idea that you can make profitable. The best is when there is one or two companies that doing things that are similar. That means there's a market for what you want. Through your spin on it.