The term enthusiast is from 1560s, pejorative, "one who believes himself possessed of divine revelations or special communication from God," from Greek enthousiastes "a person inspired." General sense (not always entirely pejorative) is from mid-18c.

A good criteria for a market is to have highly enthusiastic buyers. Enthusiastic buyers are loyal and will buy for long periods of time. A problem/solution market is different from an enthusiast market. Enthusiasts will stay with the market once the problem has been solved. Look for clubs and associations of your product to see if the product is in an enthusiast market.

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Enthusiastic, revelation from above, believe in something