Use a real bike shop

Hall of Shame | Bicycle Shaped Object

Because if you don't the cheap bike you buy could be dangerously assembled by the supermarket you bought it from.

These errors could lead to injury but they will always lead to expensive bills to sort them out.

This loks quite widespread- I have seen badly assembled bikes with forks on backwards at two supermarkets near St Albans and one in the wild in Maryshalwick.