I would suggest asking why the people want the file, and what they intend to do with it, and then base your response upon what they say. If the person would be happy with having a low-resolution or significantly-watermarked version of the file containing a notice "Full-resolution version available for license at awesomephotos.example.com", handing out such a file might provide sales leads which one wouldn't get otherwise.
If the volume of requests one receives gets excessive, one could formulate a policy, post it on one's web site (e.g. "The photos on the free-sharing page may be freely distributed in unmodified form; watermarks and captions must be left intact except when rendered as thumbnails. Thumbnails of XX size or larger must include legible copies of the full notices; those between size XX and YY must legibly incorporate [some shorter notice]. Those smaller than YY are under no obligation. Please do not ask for free versions of images not posted here; if an image does not appear here, please assume that I am either not interested in making it available, or am already working on doing so.") and then respond to any request contrary to that policy with a form letter identifying the web page and repeating the policy for the benefit of anyone without a web browser immediately available.