"And" Does Not Mean "Or"

I post this hoping to hear readers reassure me I've not lost my mind. I bought a set of salt and pepper shakers yesterday. The sign on the table read, "Salt and Pepper Shakers, $2.99."

Upon ringing them out, I am charged the price for each shaker.

"But they're a set. No one buys just a salt or a pepper."
"Unless they're connected to each other, they're sold singly."
"But, the sign says, "Salt and Pepper Shakers" not "Salt or Pepper Shakers."

My money was refunded for the extra shaker, but I had to endure being, "educated" by a teenager that salt and pepper shakers are sold singly.

Well? Is this how it is where you live, or is it just here in Idiocracy? Am I mad to expect "Salt and Pepper" means a duo? I hate being the complaining old lady, but not as much as I hate being over charged.