I am my own copywriter and have had success in this area. So here's my two-cents worth.
This is how I would find something to sell to your "yet unknown" market.
Step 1: Make a list of everything...EVERYTHING....you like. If you like to fish, then write it down. If you like to hunt...write it down. Make your list as exhaustive as you can. (The reason you do this is so you don't end up selling something you dislike. You should sell something you like...preferably, something you LOVE! If you sell something you don't like (or hate) it'll stick it out like a sore thumb in your copy. Likewise, selling something you like or love is easy. Your copy will be drugged with enthusiasm and make it an even more powerful ad !)
Step 2: Prioritize your list in the order of what you like best of the things you wrote down.
Step 3: If your first interest is say,...fishing... then the first thing to do is get your hands on a copy of the SRDS books. They have mailing lists of everything you can imagine. These books tell you what lists are available, how many people are on the list, how much they spend, etc.
How much they spend is EXTREMELY valuable info because it's not BS or conjecture. These people voted with their pocketbooks and bought...quite different from filling out some bogus survey to uncover half-truths.
Anyway, you can tell how big your market is by the figures you uncover in the SRDS publication.
As a rule, the higher the average $$ spent, the better chance you have of profitability.
As a rule, try to find a market that's ridiculously passionate about what they like....AND...(most importantly) they have money spend.
Golfers are a good example of that.
Bowlers probably "aren't" a good fit of that profit model. (They may be passionate but it's not a market that spends a lot...not like golfers or others)
Step 4: Go to the bookstore and get (or stealthily read) the magazines on that subject. (or of course, the library). Spend a day doing it. See what keeps selling month after month. That'll give you an idea of what to create or do a knock-off. And it's okay to do a knock off. It's done all the time...but you canNOT duuplicate. In fact, you can make it better. And perhaps you can make more sales because you may possibly market it better. Ask yourself, "What problems are these people having and how can I fix it?" Problems, in our world, mean profit.
For instance, if fishing is your research...and you keep reading about a problem where people are sick of fishing elbow to elbow with others and want to know where the "secret, unpopulated places" are, then perhaps you could research the "secret" places and create a CD or book or whatever revealing the "secret" fishing holes.
Step 5: See if what you wanna sell is sold on the interent because you can test for next to nothing using Google. I can't go into how to test on Google because I don't have 4 to 5 hours to write the explanation for it. But if you go to Google, set up an account you can create ads to test if people are interested.
You can set up 1,2, or 3 ads and split test their viability.
If you can't do that, you can test in magazines. It'll cost more but it's also more targeted.
Step 6: DO NOT GET A BUNCH OF BOOKS OR MANUALS PRINTED UP AND READY TO SELL!...yet
It's happened to just about all of us where we get excited to print a couple thousand copies of something only to find out no one bought. Suddenly, we have garage fodder our spouses complain that there's no room for the garden tools in the garage because those "damn books" are taking up all the space.
Instead, go a head and write up your manual. Have it exactly as you want it on your computer to where all you gotta do is email the file to a printer and have 'em print up copies you sell. Typically, it can be done on demand and you don't need inventory.
This is known as "moist testing" as opposed to dry testing (which is illegal).
Step 7: You've gotta get paid. Quite frankly, if you don't have a merchant account...you aren't in business. There are ways around it but you can't make as much money. On the other hand, if you don't have money to hold you over until you're going good, then you have to look at alternatives.
As a for instance, ebooks are a good way to go. You can sell them through "Clickbank" . And if I remember right, you don't need a merchant account for them. (But if your product doesn't sell good online that doesn't do you much good)
There's also PayPal. The only thing I don't like about PayPal is it's a pain in the back of my front to set up an account. It can, will, and does hinder sales...to what degree it does...I don't know.
Step 8: And before I'd do any of the previous steps, I'd study copywriting if I were you. It IS the key to vault.
And here's a secret lots of people don't know. 90% of your ad's success will be because of the headline.
Here's a story to relate how powerful that knowledge is.
Back in June of '04, I created an ad for a horse training manual written from the late 1800's. (Public domain material is a hot thing to sell...hey!..there's an idea)
Anyway, I wrote the ad and tested it on my site. My results ranged from squat to...well...squat.
But like a trooper, I didn't give up hope. I knew this product would be a killer product that most horse owners would love. So I kept at it.
I wrote about 150 headlines. I chose the ones I thought would do best and kept going down the list until I harmonized with my readers inner most desires.
I knew I found the headline of choice when sales starting happening instantly. I mean instantly.
I've not changed it since because nothing else has beat it.
The headline is so powerful because we are a hurried society. We don't wanna take time to read anything unless we're sure it will benefit us or it interests us in some way. (Your opening sentence, by the way, needs to be just as powerful)
The headline that finally worked has amassed me tens of thousands of dollars very quickly.
If you wanna see the headline, go to:
http://www.horsetrainingandtips.com/Jesse_Beery.htm
Whew! I'm outta breath almost...
Well, I'll shut up here but there's one other thing I want to impress upon you.
You don't have to be an expert...to be an expert. You can make yourself an expert in the eyes of the reader (which aids greatly in credibility)
When I created my horse training website I honestly did not know that much about horses and horse training.
Turns out I know a helluva lot now because I've read a lot about it, created products for it...and most importantly...I love horses!