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

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

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

General Introduction to Boundaries from Panahi Counseling:

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Serious disappointment when the client cancels a session.

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

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

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

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

Off the top of my ancient head:

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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.

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

Why do people keep saying they have evidence and have presented it that proves you're wrong even though they have none and haven't presented anything? Furthermore, what do they think you're wrong about?

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