Which character(s) have a fixed mindset?

The Crystal Merchant undoubtedly has a fixed mindset. Because of this, he doesn't realize that it's not enough to have dreams; you have to be prepared to take action to make those dreams come true. The Crystal Merchant is a Muslim and yet has never been on the Haj to Mecca. Yet, Santiago sold his sheep and quit his job as a shepherd to follow his Personal Legend.
As the Crystal Merchant's mindset is so resistant to change, he remains stuck in his ways, unable to make any improvements to his life or business. He doesn't seem to understand why his business is failing, yet he only has to look in the mirror to see the problem. It takes Santiago to suggest they build an outdoor display to attract more customers. The Merchant eventually relents and Santiago's idea pays off.
The Crystal Merchant doesn't understand—as Santiago does—that the present moment is the only field of possibility: the past is over, and the future has yet to happen. His trouble is that he doesn't embrace the present and instead allows himself to be defined by his past and a desired future that he has no intention of fulfilling. He wants to have something to look forward to in life. Ironically, this attitude guarantees that he will never have anything real to look forward to.
The Merchant's fixed mindset is largely a product of fear. Fear holds us back and stops us from taking risks. The Merchant won't go to Mecca, nor will he do anything to improve business unless prompted by Santiago. But in order to achieve our Personal Legend it is necessary to realize that the fear of suffering is always worse than the suffering itself. And that requires a mindset a good deal more open and flexible than the Crystal Merchant's.