Finding the Balance

Topic: a type of product with predictable features that address likely user needs and meet likely user price-points

        The topic should not be just a specific product, because to recommend something without considering alternatives, makes you sound like a salesperson.  It should not be chosen without considering the users' needs and price, because meeting readers' needs is the crucial test of all good writing, and everybody has a price that's "too much" and one that "sounds like too little unless the product is really good."

Audience: a type of user with predictable needs and predictable cash on hand.

       The audience should not "me" which is an audience of one (too narrow), nor "anyone who would want to buy such a thing," which is unpredictably broad until you have identified the users/readers' likely needs.

Sources: expert reviewers about this subject who do not take money from the manufacturers for praising products but actually do compare features and user needs and prices.

        The sources should not be Internet fan sites or sellers' "Customer Reviews," but people with known records of publication on this topic whose impartiality and expertise you can demonstrate to your readers.  Above all, check to see whether the sources you are considering could take money from the manufacturers, a known source of bias.