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

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.

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

What kind of person makes you think "how come there are people like that"?

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

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.”

What happens if someone fills up their car at the pump but leaves without paying? How is this situation typically handled?

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

Off the top of my ancient head:

General Introduction to Boundaries from Panahi Counseling:

What is a narcissist grandmother like, with her grandchild?

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

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

Obsessing about clients outside of work hours.

Why are white men so obsessed with Asian women? I'm friends with people from all different backgrounds but I never see my other non-white male friends obsess over or talk about Asian women like I've seen the white ones do.

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