I gotcha. I work on a lot of user-facing stuff, so if the type is somehow wrong, I generally prefer to let the user know, which is a lot easier with models.
That is sensible and is generally the approach I take in user facing code. When I have my way I have validators on all input fields in the UI to warn users of invalid input. I like them to be very specific, checking to see if a phone number is formatted in such a way that it is usable by Twillo for example.
On the other hand services that aren't actively utilizing data I write to be fairly agnostic about that data. "be conservative in what you do, be liberal in what you accept from others." is sort of how I aim.
