Something rickety — like an old shack — is shaky and likely to fall down because it's fragile.
Some buildings are sturdy, solid, and strong. Others are rickety: rickety things might blow over from a slight breeze. Rickety things are poorly designed or have just become rickety because of aging. Rickety things tend to shake, which is a sign they might fall apart any second. If you put a heavy load in a rickety cart, you might lost your load!