Now we are asking opinions on other things that for me would vary the answer. If doing it as a business where everyone should be treated equally then maybe not. If you have a full time job, and are doing online coaching on the side and one local person wants to train with you during your training then it is a one off deal, and to me I can see that as being different. However there would have to be a serious conversation about how things were going to go in that scenario. Again, I am not a professional and am in the same boat a s you regarding being more online, crunched for time and wanting to squeeze a little cash out where it can be.
Personally for me there is zero benefit to training with someone who does not push me in some way. So for me to give up some of my training time for them they would need to pay IF they WANTED to train with me when I train. Otherwise they would be an inconvenience, now if I was actually getting something out of training with them then I would not want to charge them for being a good training partner so that would end up balancing itself out sooner or later.
Again, I don't know that it is unethical to do so, in my opinion ethics have to do with intent, as well as having clear and honest communication about the service you are being asked to provide and agree to providing. However I can see how it might cause issues with other clients who may or may not want to do the same if they didn't have the option.
Interestingly enough my views may change a bit. I am contemplating going to 24Hr to train for the first couple of months of the year just to get some more hands on training under my belt it has been so long since I have done the actual hands on personal training. That and see if i can't get myself ahead just a little bit. Plus I can always sell my nutrition plans on the side since 24Hr doesn't provide them.