I interpreted the assertion there as being that you're bribing them for better service, and an argument that this is "corrupt" because there is a belief that th

I interpreted the assertion there as being that you're bribing them for better service, and an argument that this is "corrupt" because there is a belief that the service should be provided at a single price that is known to everyone, with equal quality to anyone who is willing to pay it, as opposed to favoring customers who pay extra. That said, it's up for debate whether this is a valid expectation either in the context of public services provided by the government, engagements with private parties, or both.