Check here for signs of repair. Check the battery on the right side of the trunk. Ask if it has been replaced. Check the area for signs of acid corrosion. The long-term effects of the acid in your trunk can be expensive.
Miata interiors are pretty rugged.
The black fabric seats will fade if left in the sun. Look for wear on the driver's seat bolsters where your backside rubs as you get in the car. Check the clutch and brake pedal pads. Check the door sill near the certification sticker for another sticker that tells of a replaced speedometer and check the owners manual and warranty manual for notations of a changed speedo. Sometimes this info is scratched into the paint near the certification sticker.