The first thing I do when I get a trained or even partly trained dog (be it one I have bought or one I take in for training) is let them have a go with some sheep. I think it gives them confidence that there is something familiar in their new environment. I usually do this in an enclosed area of some sort because a lot of dogs, regardless of how far along they are trained, fall back to some sort of default method of working when changing hands—or they may not want to work at all. (I have never had one of those.) I mostly have had them tighten up or be a little rash. So in an enclosed area things can keep from being out of control. I am a firm believer in trying to never let behavior occur that you might have to fix later.
My real first step in "getting with" a trained dog is to get it to go around the sheep. I am looking to see if and how much room it gives the sheep. Many dogs in their training have been taught to give the sheep proper room so this is the first thing I want to reestablish—not to keep the dog off the sheep as much as to make sure it is giving the sheep room. The place I am usually looking for them to tighten up at is the top corner they first pass when getting behind the sheep.
I am doing this without commands. Keep in mind that words and tones of voice vary so much from culture to culture that it adds a lot of confusion when a dog changes. If you can whistle the same as the previous trainer, you are a step ahead, but voice & words are tricky. (Picture a Scottish shepherd selling a four year-old trained dog to an American woman handler from the South with a heavy southern drawl. You would be saying words to a dog that it has never heard before-even something as simple as a stop).
If the dog is tight, I assume that it needed originally work here and so treat this dog like a pup–getting it to give the sheep room when going around them.
I do this in both directions also asking it to stop on balance. I DO want to teach it my word for "stop" or "lie down". I also want it to learn my command for coming off sheep right from the get-go making sure it does both.
Once it will go around sheep correctly both directions and will stop on balance, then I start adding flank commands. I often see a little panic here depending on how different my verbal commands are—tone, accent, etc. I am looking for a dog properly flanking both across from me and as it leaves my feet.
When it is going correctly both directions and starting to understand my words, I will then start sending it a short distance as a small outrun again stopping it at the top. I again look for any tight spots or overrunning or anything I want to change in how it outruns.
When it will stop at the top a little distance away, I start asking it to stop in different, more difficult places and try flanking it off balance—watching again to see if it is giving the sheep the proper room and flanks properly.
Most likely if it is uncomfortable with flanking or doesn't understand your words, it will have trouble with off balance flanks. It is easy to have the dog take a balance flank because of body language, but the off-balance will show you if the dog is understanding you yet.
Once the dog is flanking off balance, I start with a bit of driving. Any lack of confidence will show up in a dog trying to turn the sheep and bring them back or maybe diving into them. I have found that a lot of dogs know how to drive under a certain handler's command but don't really know how to "line sheep up & take sheep away". When they change hands and the support of the handler's method is taken away, they may start circling or something else.
At any of these points, if the dog isn't working 100% and the quality of its work isn't the best, stop there and "retrain" the dog. It is worth redoing the steps. You might just need reminding the dog rather than retraining it. It may just be it needs some to learn some new "Que.". Also, building a new relationship allows you to see what training issues the dog has that you may want to change. I introduce these changes early on and closer at hand rather than trying to change or fix something 400 yards away-months later. If you find you are having to "fix" something 8 months later, you moved along too quickly and led the dog to believe that was the type of work you wanted. Then its harder to fix.
I have found that this whole process can take as little as a few days or can take months. I presently own an extremely good bitch that came from Scotland last year and it took a few weeks to get her to give up her balance to reliably take a flank off balance and months to properly drive and to shed the heavier type of sheep we have here. I bought a 2 year old bitch from Wales this past October. She came over fully trained, but when first working for me was very fast—overran her outruns, was flanking too tightly and wouldn't stay behind the sheep on the drive—wanted to fold around them. She was used to working very flighty Welsh Mountain sheep and she never had to make the kind of contact needed to push sheep on a drive or anywhere. So there is a real learning curve with her. But I have retraced these steps with her as well as the other from Scotland. The one from Scotland is now a winning open bitch and the Welsh one is solid enough in her work that I can now run her this winter in some fun trials in a pro-novice (young dog) class where she is doing well.
Another thing to think about in buying trained dogs is that if you buy a bitch that comes to you bred, many bitches go through a sort of hormonal surge in energy about 6 weeks after the pups are weaned. That is about the time you are getting going with them after the pups. I have had some be absolutely wild. If you see this change in behavior that can be attributed to hormones, be patient and don't try to get too much done at that time. They settle down in a few weeks.