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

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

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

Off the top of my ancient head:

Can I use the LEG PRESS to build muscle?

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

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

Serious disappointment when the client cancels a session.

Why do flat Earthers run away like whipped dogs with their tails between their legs when asked simple questions that expose their delusions as fantasy?

Obsessing about clients outside of work hours.

General Introduction to Boundaries from Panahi Counseling:

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

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

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

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

What is the funniest husband-wife comedy team ever: Abbott & Costello, Martin & Lewis, Burns & Allen or something else entirely?

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.