Okay here's one.
A customer goes into a cafe and orders a large coffee. The customer asks "how many shots are in the coffee" and is told there is 2 shots. Obviously happy with this, they purchase the large coffee. They pay, get their coffee and leave. They come back 2 minutes later and ask for an extra shot because it isn't strong enough for them.
How much should that extra shot be? Should it be the usual price of the extra shot or should it be the cost of a small coffee/short black since it is a new transaction?
For the sake of prices:
A large coffee is $4.00
A small coffee is $3.50
An extra shot is 50c.
I personally think it should be the price of a new coffee. If the customer was satisfied with being told there are 2 shots in a large coffee, then that is what they should be given. It's like going to a takeaway shop and ordering a small bag of chips, then leaving getting to the car having 1 or 2 and then coming back and saying "actually, can you make these large chips?" It's quite cheeky!
But I don't drink coffee, so I don't actually know if there is a huge difference in the strength of coffees at different cafes if they use the same beans.