Lady Emerald Devon
Basically, Smart Gear and Smart Skills are for the Crime Scene. They'll help you find evidence.
The charming/tough skills are to interview your suspects and so are extremly important.
Like, Ran said, you'll take whatever gear you can from favours first but make a choice whether to be a tough and charming detective and put your skills points into one or the other and smarts.
The agency thing: if you're in an agency you can put on Smart Gear to check the Crime Scene then put your set of Tough or Charming clothes to interview. :)
Also, if you're in an agency, your agency members can help with the P.E (physical evidence) so you can focus more on the interview skills.
Any questions, don't hestitate to PM (Private Message).