Why is Mr. Turner hesitant about the Logans' plans?

Moe's father, Mr. Turner, says that he would like to participate in a boycott, but that he has credit at the store and that driving to Vicksburg overnight, like the Logans do, would take too long. Finally, Mama convinces him to promise that if she could get him credit and buy the things he needs in Vicksburg for him, then he would be able to stop shopping at the Wallace store.