OS X 10.9 Screen Sharing: disable file transfer On OS X 10.7 or newer (10.8, 10.9) simply drag'n'drop files between
  your desktop and remote desktop to transfer the files between
  computers


How can I disable this?
I have made restricted account just for Screen Sharing, and I don't want remote user to be able to copy files from my machine without any serious effort.
You can just remove Screen Sharing server's helper tools from here:

/System/Library/CoreServices/RemoteManagement/screensharingd.bundle/Contents/Support/*


Quick check didn't show anything bad for the rest of server functions.

Please note that after an OS X update these helpers might be resurrected.