The colourchecker is for calibrating your camera. I thought it would make sense for a camera shop to invest in a colourchecker and hire it 10 times at £20. If the checker is not damaged/touched, X-Rite says it's ok for two years.

Same with a colour meter. I have mine, but it would make sense to be able to hire one for a day to calibrate your monitors.

Well, nevermind. Thanks for your input, I'll think about that!