An exchange is when you bring something back and get something else.
An even exchange is when you bring something back and get the same thing.
I don't care if you use these wrong, as long as you're not using "even exchange" to ask me to give you the same price on a completely different item.
Here's what I do care about.
If you walk up to me with something in a bag and something else in your hand, I'm going to say, "Hi there, do you have an exchange?"
DO NOT answer, "Well, no, I'm going to return this and buy this."
Oh really? Because THAT'S WHAT AN EXCHANGE IS.