That how my Airbnb in the States is priced. But if you are searching for 2 you should see that price and another for 3, or 4, etc. If the host has it set up properly the booking settings allow for the base price for x guests and $xx for each guest after that.
And if you showed up with 4 at my property having paid for two, you would be given the options of having 2 stay, paying for the other 2, or leaving. If I find more people than are registered in the unit after check in, you all leave. My house rules are explicit regarding visitors or unregistered guests. Been there.
A bait and switch would be something like an attempt to put you in a lesser property on arrival at the same price.
Airbnb has has some trouble over the prices not including their fees and local taxes which adds up to a large percentage of people the base highly fee.