Ive previously did some research on business cards. Here is the blog post:
Compliment slips are small pieces of paper on which a company’s name, address, and logo are printed and which is sent out with goods or information, typically in place of a covering letter and they look like this:
After looking at some compliment slips, ive noticed that all the designs are really simple and nice looking as well as they all have followed their own brand style/designs. Also ive noticed that there is alot of blank space on the designs probably because its only meant to be a piece of paper that says thank you for buying something from the company which would most likely lead to it being thrown away so the designs might as well just be plain and simple (no need to waste money on alot of ink).