What are some signs that a therapist may have poor boundaries with their clients?

Serious disappointment when the client cancels a session.

Session-expressed curiosities about client details not relevant to the therapy.

Struggling with fantasies of deeper connections with clients, whether sexual or parental or other intense or intimate relationships beyond psychotherapy.

Do you remember one day, you put a deep smile on someone's face and made them very happy?

General Introduction to Boundaries from Panahi Counseling:

Eager anticipation (or anxious anticipation) of the next session in ways that distract.

Failing to mention the client in supervision/consultation, out of fear the supervisor/consultant will advise return to ordinary healthy boundaries.

What are incels doing wrong?

These items can happen fleetingly, briefly, in any therapy, but if they’re frequent, it’s definitely time for the therapist to get some good, solid supervision/consultation.

Off the top of my ancient head:

Sense of competition with persons who are important in the client’s life.

The world of the Harry Potter series is usually considered bad worldbuilding. What are some examples of actually good worldbuilding in the books/movies?

Routinely going over the time limit with certain patients, compromising the time for the next client.

Frequent phoning or texting of clients to “check up on them and make sure they’re OK.”

Disclosing feelings, fantasies, and experiences to the client in ways not related to the work the client is engaged in.

What thing happened to you as a child that you haven’t let go of to this day?

Obsessing about clients outside of work hours.