A promotion bureau or promotion company is a business that specializes in promoting your business or your brand. Don’t confuse the activities with an advertising agency or someone who makes online advertisements. Usually a promotion is a real life experience.
Promotion can be on a special event with dedicated people in company clothing and giving away free samples (also known as sampling), but can also be a special promotion inside a supermarket to get a positive feeling about your brand. So not so much as the photo in this article: someone screaming with a microphone. But just having a chat, offer something in return and create a positive vibe around your product.
For this you need people who are trained to do this, it is not only giving free samples, it is about being the right person for the right brand. Someone who can relate to the target demographics and who is able to explain why your brand is doing what it is doing.