It goes without saying that even "professionals" in the modeling industry make mistakes. They're human, too, and it isn't uncommon for models to sometimes have to go a bit above and beyond their duties in order to maintain a working relationship with their clients and get results.
To help make this topic easier to understand, below are some examples of situations where a model may need to be more "professional" than the "professional" clients they are either working with currently or planning on working with in the near future:
Reminding the Client About Stuff
Some clients have super busy schedules and tend to be forgetful. If they promised to get back to you via email or phone on a certain day/time frame and you end up not hearing from them, chances are you'll have to be the one to make contact and remind them about whatever the topic was that they were going to contact you about.
Again, it's perfectly okay to be the one to reach out to a client and restate the details of a meeting or shoot that you've both agreed to work on. This is also an opening for the client to reply back in case something has changed or if the project needs to be rescheduled.
Only take the initiative in this situation if it's been clearly past the time frame that the client/photographer has promised that you would receive your photos. Make sure to provide them with your email address in the body of your message (if they're sending you the gallery link or attaching the images) or your mailing address (if they plan on mailing you a disc with the images on them). Even if they have this information already, make it easy for them to have direct access so that they don't have to go back through previous email conversations in order to find the information they need.
Sometimes the client will have all of the information for models well in advance, as far as hair, makeup, wardrobe, location details, etc. But don't be surprised if a client gets too busy or forgets to give you this crucial information. If you find that the client still hasn't mentioned any of the nitty gritty stuff in your correspondence, make sure to ask them about it well before the shoot date.
It may seem like common sense stuff for a client to include but like I said, clients are human and prone to making mistakes. You'll find that the client will be super apologetic and explain the reason for leaving out that info. I can't count how many times I've regularly emailed with a client about an upcoming project and it's me who ends up having to ask stuff like, "Do I need to arrive camera-ready or will there be hair and makeup on set?" "Will there be wardrobe or are there clothing items I'll need to bring?" "What is the location address?" "What is my call time?"
However, that's just another part of the territory when it comes to freelancing modeling. As a business person, it's within your best interest to develop a natural ability to cover all your bases and think of things you need in order to do your job that the client may have missed.
Of course it is important to recognize the difference between a client that is "unprofessional" versus one that simply requires a bit more maintenance. With time and experience, it will be much easier to tell the difference between the two and avoid unfairly labeling someone as "unprofessional." Being forgetful to mention shoot details in an email or not being clear about whether there will be hair and makeup services on-set isn't a big deal and shouldn't make you think negatively about a client.
Not returning emails or phone calls or making super last minute changes that inconvenience you (when such results could have been avoided) are much more serious factors that would put a client under the "unprofessional" category. As with many things in modeling, these are definitely on a case-by-case basis.