(Another elaboration of something I mentioned in one of the classes)
Samples are one thing. Free stuff is another.
There's a difference between saying, "Here's something I want you to try to see if you like for future purchases," and saying, "Here's a gift I hope will benefit you. If you like it, please call me and we can discuss more ways to help you."
One appears gimmicky, another benevolent. One is an isolated impersonal event, another initiates a relationship-building process. One is a shot in the dark (at the market), another is a shot at the heart (of a potential client).
This is why giving a free box of candies to customers is usually more effective in drawing clients than a person standing at the corner serving free candy bites. One's an unconditional invitation; the other's a feeler.
This is why offering an upcoming book F.O.C. to selected influential readers (and requesting them to spread the word) is, by and large, a better strategy than giving everyone sample chapters. Because a targeted freebie is felt as personal and generous. It isn't merely a separate version of, or substitute for, the 'real' thing (which is what samples are perceived to be).
Alternatively, non-fiction authors can give the masses an option to receive the first 2-3 chapters free (via, say, email?). These chapters can outline the problem and why readers should be concerned to learn more. This builds interest and, most importantly, initiates the relationship between author and reader.
Sample chapters from all over the book, on the other hand, can feel like merely offering 'bits and pieces' for readers to 'try'. Back to the impersonal vs. personal divide.
Last example: If you're planning on giving a free car wash, it'd be better if the wash was an incentive to pay attention to a new suite of car care products rather than as a sample of the car wash itself.
If it's the latter, people usually say Thank You, scrutinize the wash and, unless they're really satisfied, say Goodbye. If it's the former, chances are they'll say Wow(!) Thank You, scrutinize the car wash less and be slightly more open to a respectful dialogue on how their more important car needs can be met.
