I would venture to guess
IF it happens it is rare. Think about it with chemicals, ink, anything that is highly re purchased it would not help a company to tweak their samples. They don't want you to just switch a product and buy 1 gallon, they want you to switch and buy hundreds of gallons over the years.....
I have been at one of our distributors in back looking at a used piece of equipment for sale, we got on the topic of emulsions and he walked with me over to the shelf in the warehouse and just grabbed the product off the shelf and said "here try it". Now, they could of gotten the best of me and maybe they have a special "sample aisle" to bring customers down, but I doubt it!