Cavendish seeds are very rare and even if you were able to get seeds from a Cavendish fruit the resulting plant would not be a Cavendish. Most people here are familiar with the Mona Lisa aka FHIA-02, the original plant was grown from a seed developed in a Cavendish fruit.
These scams are very common especially with Dwarf Cavendish, Blue Java and A'ea'e. While Blue Java and A'ea'e will easily produce seeds it's important to realize that the resulting seeds will not produce a Blue Java or an A'ea'e, they'll produce an entirely new variety.
Seeds from a Blue Java
Seed from an A'ea'e
