There are a number of reasons that would allow for this hiring without interview process for a legit company:
They have references about you from a third party they trust... but usually they would have mentioned who is it.
Junior position (in the sense that your output will pass through a senior coworker supervision). If they don't like you they will just fire you as quickly as they can. Short like a "real interview" with pay.
"Know it all" CEO that does not take HR seriously. He has seen your CV, your mails, and likes them enough to start the process. The issue is that if the CEO does not take HR seriously for this, he might not take it seriously for holidays, paying in time, etc.
The company is recruiting one or some consultor/s for a third company and does not really care... they have some contract to provide X professionals and do not really care about their quality, as long as the legal terms of their contract (titles, etc.) are met. If you are not what the customer company requires, you will be in a very difficult situation with no help from your employer.
Others (this is how they always work and so far it has gone well, they are in a hurry for X motives, etc.)
Even if the company is legit, you should try to know these specifics about the work position.
To avoid frauds, I usually prefer physical verifications, as internet presence may be missleading (a small company may have a bad website, a fraudulent one may have a better one because it needs to misslead people). Ask for:
and try to cross check with available records (calling customers, consult public records, etc.).
After that, never pay anything to the company and give your financial information only after a contract has been signed.