Shoe Evaluation
Above are the things that you should look for when buying new shoes. You want the sole to be firm in the middle of the foot. If this is flimsy then you will place more stress on your arch/midfoot. This often is the cause of plantar fasciitis/heel pain. The heel should be stable and not flimsy and the twisting motion of the shoe should be firm.
The shoe does need to offer you support. It should be firm, but not rigid. Also the structure and function of the shoe will deteriorate over time. It is generally recommended that shoes lifespan is around 500-600 miles. That may correlate to changing them every 6-12 months for some people.