why did Jonathan mistrust the officer who wanted to take his bike

Though he knows his bike is nowhere as valuable as his family is, keeping it was also a "miracle" of its own. He almost lost the bike during the war, when an army officer dressed in rags attempted to commandeer it. He knew this ragged desperate looking officer would not return his bike. Sensing a “certain lack of grip and firmness in his manner,” Jonathan guessed that the officer might accept a bribe in exchange for the bike. After the army officer complied, Jonathan buried the bicycle for safe-keeping, in the same clearing where his son and other casualties from the camp were interred.