A working (unpaid) interview is also probably illegal.
A large proportion of new grads leave their first job after a year, and I'm pretty sure most of them are neither crazy nor difficult to get along with. A bad choice? Yup, because finding a good fit is a difficult thing, and because a lot of jobs with high turnover (i.e. new grad mills) are always hiring. It's difficult to shop for something you've never bought before (in this case, a veterinary job).
You make it sound like it's always the new grad's fault, when just as often, it's the employer's fault.
A working unpaid interview where you spend the day, observing what is going on, participating in the exams (giving a listen, palpating, but never being the doctor of record) isn't illegal. If it is somewhere, please cite specific laws as I would truly like to know.
As regards your last comment, regarding fault, re-read the original post and yes employers can and are as fault as well.
The rest is not directed specifically at CalliopeDVM but more of a general overview of things from our perspective and hoping for understanding and insights.
In our humble opinion, the day long interview is a very good way of both parties getting the best possible idea of the culture of the workplace, the personalities of employer and employee, competency of staff, etc. Hiding a crazy employment environment across an 8 hour day is hard to do, as is hiding all of your worst traits as a prospective employee, there are always signs.
Our hiring process:
We are very clear with each prospect that makes it to the phone interview stage about many things, we do two: first with the practice manager (me), one with the medical director (owner - a 20 year VMD) usually on different days, each usually ends up of taking an hour - if it is going well.
If I'm suitably impressed with your personality, apparent work ethic, client handling skills and some discussion of medical knowledge as it relates to your ability to communicate an overall plan to a client, then you get to speak with the medical director who does the same thing, also discusses medical philosophy and our way of dealing with clients: high communication, high service, high quality medicine (as close to internal medicine referral standard as possible). Referrals to specialists are fine.
We make it clear that this is veterinary medicine. We schedule for a normal day (5 - 8 hours hopefully or 4 - 10 hour days), 30 minute appointments but stuff happens sometimes toward the end of the day and don't plan on getting off at the 8 or 10 hour mark. If you get behind, you need to finish up, get your charts done, that day, before you go home, no stacks of un-done chart here. We also make it clear that we are looking for an intelligent, pleasant person, who wants to contribute, wants to learn, has a good work ethic, that we are really fairly reasonable people, are willing to listen to ideas and suggestions, open to discussions of almost anything, are willing to share almost anything about the business. We point out that if you are scheduled for an 8 hour day, that means you are at work for 8 hours, plus time off for lunch (30 minutes or an hour), plus your commute time which means in this area you could be away from home 10 1/2 plus hours each day (or more) depending on where your choose to live.
Only then might we suggest an in-person interview which is where the day long visit (working interview) comes in.
You pay your travel - shows some level of commitment.
We take you to lunch as part of this process.
If we like you, we make an offer, and if you like us, we settle on terms and send you the contract for review. All of the below people had contracts. Comment: The contract has escape clauses for both parties. FYI: No contract can overcome any lack of good will from either party. We assume you have good intent, as do we.
BTW: You get lots of mentoring from the medical director and the staff - way more than most places give.
We have two new grads, one almost a year now and one three month in, who are great, we hope they stay forever and that we can continue to find them professional growth. We understand that for various reasons people might want to leave or become unhappy with some aspects of their job. We say straight up, if you are unhappy about something, please let us know and see if we can find a solution. We'd like an open discussion and not learn abruptly one day that you are resigning.
Oh for those relocated, we offered many suggestions about the area as to where to live and where they might find an area that might fit their interests.
In short, we bend every effort to find and keep a good fit.
Some more specific comments regarding actual events (no names used):
Our first hire out of a well regarded school said they were very flexible, after hours were no problem if needed. Turned out they were a loose cannon, showed up day one in inappropriate dress and didn't realize it, had to be told how to dress (now we are specific about dress), was married to a spouse whose father was a vet. That spouse resented (hated) their father for having to work long hours at his own practice. Needless to say, this cause issues when the new hire was always running way behind and getting out late because they were not very organized in their work - we tried to help with this. Staff was always having to clean up their messes. All this got worse as time progressed, was chaotic, let them go in less than two months. Sad because their medicine was fine.
Second hire was a vet who had a couple of years experience Banfield and a few other places as relief. A high energy person who was a decent vet. Had some issues with getting behind but this improved as we discussed the specifics how each appointment went. A debriefing if you will. The fatal flaw was authority figure issues. Would not speak to owner (medical director) after being told they were flat out wrong about something, would barely interact. Not a workable situation, tried to make it work, had to let her go after a couple of months. This person later said it was the best job they ever had.
Number 3 is our (almost) one year vet - doing great, likes the job.
Number 4 was back and forth about being interested, had good references from mentors, etc. Had some stated interest in public policy aspects of vet medicine. Came for interview, we offered position and accepted, moved to area with fiance who already had a job in the area. Both new grads. On day one, called at 8am, said they had a flat tire could make it in by 11am to Noon. Sigh. Fine. Understand, stuff happens. Then we find was completely uncomfortable with doing anything, e.g. wanted to see how medical director did vaccines before doing it themselves. Almost had a heart attack on day two when asked to visit a nearby boarding facility as a house call for dog with apparent kennel cough (They were having an outbreak at the time). Medical director told them exactly what to do. Day Three called up and resigned, saying we were unprofessional, etc. We think the flat tire was a conflicting interview for the job they really wanted and was offered the job. We think only took our job as fiance already had job in area and choose to live one hour away from practice (not a good sign).
Number 5 is three months in, doing well, likes job more than expected.
Number 6 lasted less than two months. Saw lots of cats and dogs with middle ear infections that no one else saw. Liked Clavamox for those. Cat with slightly elevated BUN, normal creatinine, would put on Purina NF, maintained they had kidney disease, their method of client communication and characterizing a cats status lead two clients to euthanize. Hire Number 5 was very upset with hire Number 6 as Number 5 spent the weekend syringe feeding the hospitalized cat who was on IV fluids and was starting to improve. Number 6 decided to "tell the client the truth" and the cat was euthanized.
At that point, we asked ourselves and Number 3 and 5, would we be comfortable having Number 6 treat our personal pets. Answer: no. Number 6 was fired. Sigh.
At a personal level, we liked Number 6.
As an aside: Number 5 was on that weekend in case anything was in the hospital or the boarding facility called. The medical director is in the rotation as well - fair is fair.
So, we try as best we can to find a good fit and have learned more and more quickly to recognize as bad fit and end it quickly to the long term benefit of all involved. Hiring is not easy especially if you care about more than a hiring a body with a pulse.
That sucks RRT. Sorry to hear it. Hope the job search goes well ... really sucks worse since you liked it there. 
