Yeah not sure why any professional would request monetary compensation for pictures?
It's free advertising for you, plus if I was in business I would want my work out there pending it's quality so people could vouch for me. I've referred dozens of people online to local detailers I've found on here and Autogeek because of their pictures and detailed work I know I can trust them. Additionally most of the people that are active on here either are professionals or hobbyists that take care of their own vehicles. They don't need to see photo proof of your work it's just a community that likes seeing each other's work and is here to help one another and newcomers.