Consumers have many choices when they buy a product, including buying a competitive product, buying another type of product or buying nothing at all. You need to be confident people will select your product from all these possibilities before you decide your product is a winner.
In the case of Clean Shower, Black gave product samples to friends, relatives and acquaintances and waited to see if they would ask for more. People had to come back and insist on getting another bottle of Clean Shower before Black could feel confident his product would sell.
If your product can be made only after a large investment and providing samples is impractical, you can still offer people a choice by showing potential users a series of products already on the market--along with your prototype--and asking them to rank the products by how likely they are to buy them.
One product I evaluated this way was the Dish-Net, a net that could be used in dishwashers to keep plastic cups, bottles and caps from overturning or falling into the dishwasher's heater core. I called a local women's group and invited them to participate in a market research group for the new product. The group was happy to participate at their next meeting, which was attended by about 40 women.
Because the product had only one indirect competitor, a dishwasher basket for small items, I displayed them both, along with four household products that were about the same price: a milk-bottle spout, a microwave bacon tray, a set of plastic storage containers and a lint-removing brush.
I asked the people to rank the products by how likely they were to buy them. I'd consider marketing the product if 20 percent of the participants ranked the product as a first or second choice. That may seem like a low percentage, but 20 percent of the people ranking a product first or second is a very strong showing if all the products are already on the market. In the case of the Dish-Net, 30 percent rated it as the first or second product they'd most likely buy.