I work at a used sporting goods store that sells used weights (plates or dumbbells). There are clearly marked signs that tell you that used weight is $.70 per pound. Each weight also has a tag on it that reads "Used Dumbbell $.70/ lb". If that's too confusing for you we have also printed multiple signs that tell you how much each increment of weight will be in dollars ($7 for a 10lb dumbbell).
This should be pretty straight forward, and for most people it is. At least once a day though we get some genius that has never been to a produce aisle that brings up a hundred pounds of weight, says sarcastically with a big chuckle "I'm getting away cheap today!" Thinking their total is going to be something like $2.80 for their 4 dumbbells and then I tell them it's $70 plus tax and they look at me dumbfounded. Some people even have the balls to tell me the sign is misleading, when in fact it's that they just aren't reading.
I'm sure most grocery store employees have dealt with this phenomenon before. But do people really think a 50lb dumbbell is the same price as a 5lb one?