Forms should stick to certain ethical principles: you should never ask for information that is not absolutely required; your privacy statement should be simple, free of legalese and stringently kept to. But one dirty trick that some clients insist on integrating into forms should be given particular attention, and rigorously avoided by developers.
The technique as commonly called “opt out”. I refer to it as “implied consent”. The idea is simple: users of forms are often rushed, not very bright, and tend to skip over form elements that appear to be completed for them. “Implied consent” uses these factors to trick people into consenting to something that they would otherwise say no to.
While you’ll never see an example as blatant as what follows, it’s a good sample of the type. The scenario is this: you come to a form and start to fill it out. Somewhere near the bottom is an element that looks like this:
(More frequently the statement will be something along the lines of “Subscribe me to your eMail newsletter”).
Note that the checkbox is on by default, due to the checked attribute being used in the HTML. If the customer is in a rush, they will skip over this… and by not explicitly saying no, consent is implied, and they are a target rich for misuse. This does not work in relationships, and it should not be a part of forms.
The inverse is also frequently used:
In this case, the implication is that not checking the box will lead to spam flooding your inbox.
“Implied consent” can be a good thing when it is in the interests of the customer. An example would be the assumption that the user does not wish certain to share certain information publicly, such as their eMail address. While doing so may give them some added benefits, it is an option that the user may take into consideration, and the assumption should be that they do not want this feature on.
Bottom line: don’t trick people into filling in form elements. Customers who actively sign up for your newsletter will appreciate it more; those who were fooled into doing so will (rightly) tend to regard you with distrust, suspicion and anger.