I evolved a favorite response to free requests. If made in person, I'd observe that the requester was driving a really nice car, and I needed one. Could I use it for a couple of weeks while I put together a list of images for them?
If made online or on the phone, I'd suggest they send me a free new laptop so I could process their request for free products.
Always seemed to set the conversation on the right footing. If they turned me down, so be it. If they didn't want to loan me their car or buy me a top end laptop, we could certainly discuss image licensing fees instead.