Mack Collier of The Viral Garden has articulated why it is wrong to ask experts to speak for free, saying that good speakers spend days creating material and preparing for a presentation. He estimated that he spends "anywhere from 15 to 30 hours preparing/rehearsing the presentation, and loses a minimum of one day due to travel, usually two days."
This is a big investment of time for anyone -- and for experts, time is money. A good event organizer will not ask a speaker to speak for free and they will cover travel costs. Speakers understand the need to offset costs by giving speaking slots to sponsors. But sponsors are advertisers. Just because someone paid for a sponsorship doesn't mean they have the expertise you need.
As someone who has organized numerous events, my goal is to secure speakers who provide the expertise participants will benefit from. The speaker's expertise should be lending credibility and value to your event. Framing the event as a business development opportunity for the speaker is unprofessional; the reason to select speakers is for the value they bring to your program. A good speaker is not there to make a sales pitch; rather, to educate, entertain, and/or motivate the audience.
The second request is to substitute a customer as an expert. The underlying message is "you are good enough to do the work for a company but not good enough to speak at our event." This request places the experts and their customers in a very difficult situation -- who pays for the customer's travel since many companies' travel budgets have become restrictive, who prepares the presentation, who preps the customer since they are not experts, how do they handle Q&A's, what if a company commitment comes up and they need to bail, and so on.
This kind of request often results in the experts paying travel for both the customer and themselves, preparing the presentation since the customer doesn't have the time or expertise, and having do a dive and catch when the customer has a last-minute schedule conflict. It also creates schedule challenges for dry runs, which can negatively impact the event attendees' experience.
It is easy to see that this particular request creates an enormous amount of work and additional costs for the experts and additional work for their customers with no payoff for either party. In today's environment, customers want to use their limited resources to reach their prospects and customers, to grow their businesses. Their time is money, too, and they want to invest where they will see the best return.
If you want to be a better event organizer, stop making these two requests of the experts who can add tremendous value to your event.