Why do you think Walter changes his mind in regard to Mr. Lindner's offer?
Walter changes his mind in regard to Mr. Lindner's offer because the $6,500 his mother gave him ($3,500 for Walter's intended liquor business and $3,000 for Benethea's education) has been stolen by Willy Harris. Instead of investing only the $3,500 for the liquor business, Walter secretly included Beneathea's share into the liquor enterprise. When Bobo announces in great anguish that Willy has absconded with the money, everyone is furious; Mama physically attacks Walter and berates him for what she considers his dishonesty and lack of accountability in regard to his father's hard-earned money.
When Mr. Lindner (from the Clybourne Park Improvement Association) comes calling, everyone is initially suspicious of his motives. Mr. Lindner has come to make the family an offer: the whole housing community is prepared to buy the family's new house in Clybourne Park for a higher price than the original amount paid for it. Mr. Lindner tells Walter and his family that the community is uncomfortable with a black family moving in, believing 'that for the happiness of all concerned... our Negro families are happier when they live in their own communities.'
Mr. Lindner's original offer is turned down. However, after Walter discovers that Willy has stolen his money, he reconsiders his earlier opposition to the deal. He argues with his mother that the world is made up of those who take and those who get taken from. He reasons that Willy's treachery has taught him one thing: that it's time for him to take what should be his and to give his family what they deserve in life. To that end, he intends to accept the money from Mr. Lindner.
However, at the last minute, Walter changes his mind. He tells Mr. Lindner that they have always been a proud family who will work for everything they want in life. With his son Travis by his side, Walter reiterates that the family will move into their new house in Clybourne Park because his father worked for it and earned it for them brick by brick. Walter promises Mr. Lindner that they will not make trouble for anybody in the housing community and that they will try to be good neighbors. With Mr. Lindner's departure, the family prepares to move.