@Clare0, in addition to being an AirBnB host, I am a network administrator and a server admin.
Please be aware that the word "secure" when used in reference to "https" only really means that the connection uses encryption. It does not mean the site is "safe". Using the word "secure" implies a sense of safety. In this case, that is not what it means at all. It just means the connection is hard to eavesdrop on.
So while having a "https" does indeed indicate that a connection is encrypted, it is no way guarantees that a site is legitimate. Whoever set up "http://airbnb.com-online-booking.eu" could very easily have set up "https://airbnb.com-online-booking.eu" as a "secure" version, but still a scam.
In addition, NOT having the https, does not mean a site is a scam. It just means that they allow connections that are not encrypted.
For example, I sometimes visit a news site: http://tidbits.com. They have been around for 28 years. They are definitely not a scam. But they choose to not require encryption when connecting. Most of the sites I administer choose to not require encryption except on specific pages dealing with credit cards.
There are scam web sites, and there are legitimate web sites. But looking at "http" or "https" really is not a good way to tell the scams from the legitimate ones. At all.