Make sure their preset name is typed exactly like their username, it is very case sensitive; Example:
Username: PrEsEt
Preset name: PrEsEt_#.fhp
--- If they do not match, the preset will not show up! Edit: and you will have to ask them to export it properly. To do this they need to open the game, type their username exactly as others see it in the username field, but not log in... then go to preset maker and export again.
Also, if you do not have preset sync: Simply place the .fhp in the "presets" folder.
If you DO have preset sync: Place manually obtained .fhp's in the "privatePresets" folder.