I have had to build things I consider to be dark patterns. Normally, it goes something like this:

1. Client asks for something that is a dark pattern.

2. I outline that it is morally questionable to do that and give a suggestion on how it can be done otherwise.

3. Client insists that they don’t care or don’t agree because they feel as it will bring in more money.

4. I end up building it.

I do have the choice to outright say no, but I’ve found that it normally comes down to a compromise. Some clients are not willing to budge but we can always steer them in the right direction.