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

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

Serious disappointment when the client cancels a session.

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

Is it common for girlfriends to have close male friends who are single and not related to them?

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

General Introduction to Boundaries from Panahi Counseling:

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

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

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.

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

Off the top of my ancient head:

What's your favourite porn video to jerk off to?

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

Obsessing about clients outside of work hours.

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

How much of lounge pianists playing is from repertoire, and how much is improvised?

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