The greatness of the Devi Mahatmyam is extensively explained in several texts such as Rudra Yamala, Marichikalpa, Meru Tantra, Kataka Tantra, Chidambara Rahasya etc. The Devi Mahatmyam has the ability to grant the fruits as per the upasana.
A sakama upasaka (one who does sadhana with a specific desire or goal in mind) achieves whatever he aspires.
A nishkama upasaka (one who does sadhana without any expectation or desire) achieves moksha, as revealed in the story.
Suratha the king was bestowed with unmixed prosperity whereas the merchant Samadhi was conferred with divine knowledge according to their own aspirations.
If Sri Candi is pleased, She Confers on Her devotees both earthly prosperity as well as supreme knowledge (sā yācitā ca vijñānarh tu1tā rddhirh prayacchati, DM, 12. 37).
Matsya Purana prescribes recitation of Candi three times for cure from physical ailments, five times for relief from malefic planets; seven times for relief from impending disaster; nine times for ensuring peace; eleven times for winning royal favours; twelve times for overpowering foes; twenty five times for release from prison; thirty times for cure from cancer; a hundred times for relief from great dishonour; one thousand times to mitigate loss of wealth and for steady prosperity etc.