You might be looking for a different word here. A dark pattern is not fraud or outright lying. These are already illegal. Seeing the total price at the end of the purchasing process is the legal requirement for a sale.
A classic example of a dark pattern is AirBnB. They (used to) show listing prices without all additional fees like cleaning, service fees, etc. So users would end up wasting a lot of time on finding the right offering to only later (yes, before checkout) realize that the total price is actually much higher. Users know how much they end up paying, it's not fraud. But this is still a dark pattern.
Well, I'd argue that you're looking for a different term, but obviously there's no concrete definition here.
I don't think a dark pattern requires any fraud or lying. I think the most obvious example is having users opt in to something (e.g. sharing private data) by default and only offering the option to opt out by navigating some convoluted series of menus. You aren't explicitly lying to users and telling them they can't opt out, but you're going out of your way to make sure the option isn't advertised or easily accessible.
In my opinion, there's a gap between that and what airlines and AirBnB do. I guess there's an element of deception with both, but airlines and AirBnB are just waving a nice number in front of your face to drive engagement. That doesn't personally meet my threshold, but I understand how it might meet yours.
For all that Booking.com has lots of annoying patterns like telling you how many people looked at a listing and that there's only two rooms (currently) available for those dates, I do like the fact the price I first see in the ranking is what I pay. Not least because the AirBNB fees usually seems to be how much more it costs to book with them if they have a listing for the same place.
>Booking.com has lots of annoying patterns like telling you how many people looked at a listing and that there's only two rooms (currently) available for those dates
Assuming they're not making up the data, why is this bad? If a hotel is very popular and almost sold-out, isn't that something useful to know when you're making reservations? Sure, it does feel a little high-pressure, but if it's truthful (normal "high pressure sales" tactics aren't, they create a false sense of urgency when in fact there's no shortage at all), it can be useful if you're trying to book a room at a popular place or during a peak time.
In practice I think it's usually inaccurate for medium sized hotels not because Booking.com makes up the data, but because the hotel doesn't release all its inventory to Booking.com at once. Otherwise it's not bad per se, but in combination with the "two people looked at this listing recently" in similarly red letters and all the book now pay later stuff, it does feel a bit like booking with someone shouting at you to hurry up
A classic example of a dark pattern is AirBnB. They (used to) show listing prices without all additional fees like cleaning, service fees, etc. So users would end up wasting a lot of time on finding the right offering to only later (yes, before checkout) realize that the total price is actually much higher. Users know how much they end up paying, it's not fraud. But this is still a dark pattern.