PET disadvantages of unstructured interviews:
Practical: Time consuming to train, arrange and conduct, can be costly (i.e. venue, training, often paying the interviewee), researchers need to be highly skilled.
Ethical: Sensitive topics may cause distress.
Theoretical: Risk of interviewer bias which affects validity so must be carefully planned, social desirability may occur, open questions are an unreliable method, unrepresentative data as its opinion based and is small scale.