I give customers a sample for every $40 they spend, my choice, although if they ask for particular things, I do my best to accomodate that. Samples are free. They are usually a very small amount of a product I make in a less expensive package.
Sometimes I am asked if I will sell only samples to someone. I haven't done this in the past, because it seems like the same amount of work for a lot less money. Widgets do have pricy ingredients, but the labor of making and packaging them is more costly. One item I sell a lot of is sold in a similar form by a very large site. Their price is 17.50/5ml; mine is 13.50/7.5 ml, so mine is substantially less. They sell samples of many of their widgets for $4.00 for 1 ml, same size as I give for free with every $40 of purchase. Their shipping for this tiny size is steep (IMO) at $7.50, so I'm thinking they are making some money off that.
I'm not sure if it might not be detrimental to sell samples. Even though it might mean that people would try more, at $4 ea, they would get four sample widgets for the price of one widget now. I get people who order 4-5 widgets without batting an eye. These people might decide to order 4-5 samples instead, which would be a substantial decrease in order total.
The other thing is I know that there are people who do nothing but trade samples they have bought from my primary competitor. There are whole websites devoted to trading these samples and they are sold on ebay as well for more than was paid for them. That does spread the name of the original vendor around, though.
Personally, I tend to think that selling a sample size is a stupid idea. But maybe I am just being blind. I could use some feedback.