I'm an Architectural professional.
Some people hire Architects.
These are two things that people regularly have no objection to paying for. Admittedly the travel agency profession has changed. I understand that they're generally paid by the companies they book with and the customer isn't charged any longer.
Any information on rates, fees, or cost as % expenditure would help.
If you have your own data that you're willing to share, that would be great too.