Salty snacks like peanuts and pretzels can often be found for free at gatherings where beverages are for sale. Vendors hope that the salty snacks will make consumers thirsty so they will purchase something to drink. Why does this work

You have to consider the invesment that vendors make to buy all above-mentioned peanuts and pretzels ... Also, you should ask yourself this:

How many either pretzels or peanuts I need to eat to start feeling thirsty?

Let's say it's a trade strategy ... What do you think about?