A book called the "Four Hour Workweek" outlined some great strategies for inventors to test the sales of any product or invention. Thanks to the handiness of the internet, you can test sales after just a few weeks and under $500 spent. I've paraphrased the steps for inventors below:

Determine the Margin

Determine the estimated profit of your product. You want to choose a product that can sell for at least 4x what it costs to manufacture. 

Research Keywords

If the product passes the margin test, come up with some terms people will use when searching for your item on the internet.  Try different variations. Use Yahoo's Search Marketing Tool, Google Adwords Keyword Tool, or Wordtracker to help you come up with alternative phrases and see what's searched most often.

Research Competitors

Use the most searched terms from above, pick three competing websites that most consistently appear in the top of Google search results.

Then visit each of these three sites and note:

• What you like/dislike about the site
• What they offer
• How your site, advertising message, and product pitch can be different using. Consider differentiating by:
• Testimonials
• Selling more products
• Photos
• Shipping options
• Guarantees

Create Your Advertisement
Using the differentiation message above, write an advertisement that emphasizes what your product does differently, it's benefits, and photos.

You can use advertisements from magazines or the internet that you have found compelling.

Test Pricing

Test your concept with a short Ebay auction with the advertising text from above. Set your minimum price for what you'll accept. Then cancel the auction at the last minute to avoid any legal issues (since you don't have a product to ship). That should give you what price people are willing to pay in the marketplace. Again, apply the margin test to see if your invention passes.

Test Sales

Create a simple 3 page website with cheap hosting and a good domain name. You can hire someone for a few hundred bucks if needed. The pages should be laid out like this:

1. Advertisement page with a purchase button at the bottom - no pricing
2. Pricing and order form, shipping information, basic contact info
   
3. A page telling the customer you're currently out of stock
   

Advertise using Google adwords with a budget of $50 per day. Run the ads for a week.

Moment of Truth

After a week, you should tally the results. See if you made more "theoretical" sales $$ than you spent on advertising.

Play with the pricing, try different guarantees or shipping options. But at the end of it, you should have a much better idea if your product will sell and how much it will sell for. 

**As with any time you're disclosing your invention to the public, consider patent rules governing public disclosure. If you have applied for a provisional or utility patent, then you should be okay following the steps above. However, if you haven't applied for any  patents, then keep in mind that current rules state that after public disclosure, you must file your patent application within 1 year. Consult a patent attorney for more information.

---