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

Off the top of my ancient head:

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.

Why do people stay in cults after they have joined?

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

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

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

Can a cop pull you over walking home asking why you are out so late?

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

General Introduction to Boundaries from Panahi Counseling:

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

Can you write a short story with a twist ending?

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

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.

Obsessing about clients outside of work hours.

Would you let your partner cheat on you every now and again?

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