Officially, "type dynamics" refers to the way a person's preferences interact with each other and develop. It includes the order of preferences as a tool for describing development/motivation/dominants. It explains why INTP and INFP differ only on one letter but couldn't be more different in their core approach to decisions. And why INTJs and INFJs are more similar than the previous pair. And why Si looks different in ESTJ and ISTJ.
As for how type practitioners go about it...it isn't that we think the person is always an adequate source of information but that we don't have the right to tell another person what type they are. It usually backfires, anyway.
Again, ethically, whether done with groups or individually,
- The type practitioner introduces the concept of preferences--we can do both, and develop skills, but have a preference for one end of each dichotomy over the other
- We explain the theory, whether it is our preference to introduce it through the preference pairs, the 8 functions, or begin with temperaments. There's no right way, just varying degrees of skills, interests and application needs among practitioners.
- Ideally, there is also time for exercises--short experiences using the preferences that are designed to help the person discover preferences over learned skills
- The person self-selects their 4 letter type code
- The person is then given their results from a validated type indicator, be it the MBTI, the Golden, the PTI, the JTI, or whatever
- The person and the practitioner work through interpretation of any differences between self-selected results and reported results
- If the person believes he/she has figured out best fit type, the practitioner provides a full type description for the person to read. Often the person also wants to read another type, such as both ISTJ and ISFJ, for further verification
If I don't think a person has correctly identified his/her type, usually there is no point arguing right then and there. But as a workshop goes on (this first part should ideally take at least 3 hours), most of those people have aha moments, especially if the trainer is skilled at ensuring that every preference is honored and the group comes to see how the best type to be is your own type...