Final answer:
The sales promotion method where a manufacturer provides small bottles of shampoo as free trials to houses in a neighborhood is known as 'a sample'. It is aimed at increasing product awareness and encouraging purchases.
Step-by-step explanation:
When a manufacturer places one small bottle of shampoo in a clear bag and hangs it from the door of each house in a neighborhood, this type of sales promotion is known as a sample. Samples are a promotional strategy used to introduce potential customers to the product by providing them with a small portion or a trial size to try out, usually for free. By doing this, the manufacturer aims to increase product awareness and stimulate consumer interest and trial with the hope of leading to product adoption and purchase.