Be careful of individuals who approach you to be your guide.
Unique Suggestions: Best is to approach CAMAT( Chitral Association for Mountain Area Tourism) a UNESCO project which is conveniently located in the town center. Phones 413540 and 413708. Also know that trekking guides are supposed to be licenced by the government so the least you should demand from any one is his licence.
Fun Alternatives: Involve the hotel where you are staying to recommend a guide to you rather than picking up individuals at the airport or shopping center.