Upload & Sell: Off
Nothing wrong with using a telephoto for full-length portraits.
If the subject is 'unrecognisable' there are a couple of options to make his face bigger
1. Crop to remove empty space around him. Should be plenty of pixels available
2. A more 'compact' pose such as sitting or kneeling so his head occupies more of the frame
3. Head and shoulders rather than full body
Personally I can't see much wrong with your shot, not sure what she's complaining about.