I did that once. Made a thousand dollars for my efforts when it closed down. As long as the expectations are not too serious and it is not a crackpot idea, why

I did that once. Made a thousand dollars for my efforts when it closed down. As long as the expectations are not too serious and it is not a crackpot idea, why not? I have a main job so as long it does not interfere with that, all is well.