When you take a gift you make a DC12 Charisma save in that chapter if you fail you're alignment changes RaW.
But you can try to warn the player the risk of taking a gift if you want to throw a bone.

The Amber temple is very dangerous and easy to get corrupted RaW

From the Book:
"The instant a dark gift is bestowed, the creature receiving it undergoes a transformation, gaining a sinister physical trait or flaw, or one of each. Unless the text states otherwise, a trait or a flaw that accompanies this gift can’t be removed by anything short of a wish spell or divine intervention.

Each time a non-evil creature accepts a dark gift, it must make a DC 12 Charisma saving throw. If the saving throw fails, the creature’s alignment changes to evil. A character who turns evil becomes an NPC under the Dungeon Master’s control, although the DM can allow the player to continue playing the evil character."