What's the best way to recognize a good business opportunity?
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There are a lot of factors other than marketing that you'll need to address, and you'll need to find out what factors in your marketplace will allow you success. Basically run a marketing analysis and get some research done to be sure it's worth going for.
It can be a great idea if the market is willing to patronize your establishment. You'll also have to figure out what you're going to do that will make your restaurant unique (if you haven't read "Purple Cow" by Seth Godin, you should).
A business plan will be the final tell-all as to whether or not it's a good idea. Bottom line, don't go in blind, if it feels right find the data that will justify it and other data that will present challenges to overcome. A S.W.O.T. analysis is definitely needed.