This is an important and interesting moral and ethical dilemma, isn't it? Should you feel sorry for the business owner and not point out negatives? Or should you care about someone who has worked hard to earn enough savings to buy a $2,500 amplifier who wants to know the full truth and not a censored one.
I remember reading a Yelp restaurant review. The person end his review exactly as you say, "well, this is a mon and pop business and I will be the last guy to try to impact their business so I give it four stars" or some such thing. At first I thought that made sense. But then I remembered how often I rely on these reviews to find a restaurant when I am travelling. And how disappointed I would be to have a lousy meal because something thought they should take the side of the restaurant owner than my need for unbiased and unabashed review. So I write all of my Yelp reviews this way. If the food is bad, it is bad. If the service is bad, the service is bad. People are entitled to reliable and good information. The moment we corrupt the nature of this, we can't trust anything and the system falls apart.
As you say though, everyone needs to decide for themselves where they stand. Once they do though, I like to know that front and center. If you tell me you are a reviewer but then go on and only write positive things because of this or other motivation, just tell me. I will still read and care about what you say because you bring information to us. But I would not rely on it for purchase decision because I know you are loathe to say anything negative. Peter's videos fall in this category for example but sadly he never indicates so.
Andre just gave you a thumbs up for your post. I assume it means that he will side with the equipment owner and not try to point out negative things. If that is not the case, then I am not sure why he is agreeing with you.
It is this kind of ambiguity which I think is improper. As I said clearly and repeat, I am on the side of us, the consumers. If equipment is not designed right I am going to say it. I wrote my inside AVR/BD player for a magazine that makes a living from the very same advertisers. The magazine publisher not only had no problem with this, but loved and has encouraged me to write more. It is who I am. When people look at my name, that is what I want them to think. That I will be critical and I will point out issues with products. That way there is no ambiguity and reader can tell what to do with the information to share.
While we were discussing the Regen product, I was approached to review a linear power supply. I told them right then and then that they should not send it to me if they have any expectations of how it may come out. To their absolute credit, they were 100% cool with it. And as it turned out, my review was not positive on the product. But hugely positive on the company. They did the right thing in wanting their product tested. And I think I did the right thing by not covering that up simply because I was loaned the equipment for free.
I learned a lesson long time ago from our corporate attorneys and it is the concept of "bright line." When something can be a matter of interpretation, their advice is to stay so far clear of the issue that it then becomes black and white. Be 100% respectful of female employees and then you never have to worry whether you have or have not violated sexual harassment laws. Such is the case with me. I will 100% positively on the other side of the bright line. I am an advocate of us the consumers, not the manufacturer.
Now as to dealing with friends, man that can get tough and awkward. What would I say if someone asked me what is wrong with Steve's system? My answer would be to go away

. I have not solved world peace. But have only figured out how I conduct myself when the situation is not so personal.
Would be interested to know which version of an equipment reviewer members like to see. The one that cares about the owner or us.
BTW, I own a small business but absolutely do not expect anyone to sugar coat our performance. If we do something wrong, I want to know and fix it. I don't know how to have a quality company and services otherwise.