It is a common fallacy that flat shoes are necessarily better for you than high heels but this is not strictly true. Whilst most of us appreciate the perils of constant high-heel wearing it's not readily known that some flat shoes can be equally as bad for the body.
Cheap flat styles that don't have a contoured insole or that lack a sidewall to support the arch of the foot can lead to problems including bunions. They may also transfer impact to the legs and spine. So pay attention to looking for pairs with a well constructed inner with a moulded insole and a slight heel which will increase comfort and lessen impact on other parts of the body.