Utube reviews hit or misses accuracy

I have been watching Utube videos vs say reviews in Tas magazine ,Stereophile 
or other online reviews .on utube  like Zero fidelity ,or the next best thing studio
they give a review , and what they misses entirely for example they don’t try different power cords to get the most out of them ,as well as same a premium synergistic orange fuse which is crucial on some power supplies especially with class D hybrid variants, and class AB .The new Marantz ruby for example is technically the same $4k as the new Model 30 internally and it can be noticeably improved 
upon is for whatever reason switch mode power supply removing the steel fuse opens it up nicely.. More of depth , as well as a heavy power cord .I have a awg 7 Anaconda and the transparency and depth really improved vs the Luxman 505 mk2 which is a class A design it naturally is very transparent but not quite as nimble or fast.
I owned an Audio store for a decade and truly have many hours at least in matching listening over 40 years .to do a proper audition you need to match the correct power cord to That given product .I found 
many products including vacuum tube that truly open up just by experimenting with power cords .
these online reviewers should tell you what cables they are using, and a must to use the exact speakers and sourse ,or there comparisons are faulty. Even in magazines I have found they will do a review and comparisons but use a different brand of cables or mixes ,That is why I have found you can get a solid 10-15improvement by matching the cable for its warmth and depth ,or transparency speed or detail. With digital sometimes a night and day difference stock power cords Never should be used in a review 
I see blue jeans cables, in reviews that’s fine for a entry level $3k system not a $10k +.
cables can be way over priced you need to do some research . myself spend sometimes 10 hours just in reading on a specific  product 
and try to buy with a return option ,system synergy is not always guaranteed ,that is one thing not
tslked about enough ,just buying all A category products doesnot guarantee it will sound coherent .
i have had to some times goes through 3 dacs ,or amplifiers before I get the right synergy.
loudspeakers I always upgrade the Xovers for the vast majority even in $20k+ speakers the capacitors resistors are often not much better then average .having modded speakers for over 20 years .I know how to voice to get a more natural tonal balance ,on average oly  25%of the cost  is all that goes into your equipment the rest overhead ,markup,dealer markup.
modding brings the best bang for the buck. On All gear.

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I always have felt it was important for a reviewer to use and describe the component he/she was reviewing in its stock form; after all, that is the way it will be purchased by a consumer.  After that, if they want to experiment with power cords, cables, footers, etc. they can do so and describe the changes (not necessarily improvements) that they hear.  But I vaguely recall a reviewer years ago (not sure who or what he was reviewing, but I wouldn't be surprised if it was Jonathan Scull)  once reviewing an expensive piece of equipment and not waxing ecstatic until he added some tweak that cost almost as much as the unit he was reviewing.  That implied to me that the unit stunk and wasn't worth its asking price.  And while modding a unit can provide good bang for the buck, then you're not describing the component that is being sold to the public.

I do agree with the OP that working to find synergistic components and cables is important and should be part of a review.  That's why I find Herb Reichert's reviews in Stereophile to be so good, he uses different speaker/headphone/amp combinations and compares and describes them, thus warning his readers about possible mismatches as well as good combinations.
Whoever says you can’t tell the difference between power cords 
Either has a cheap system or something wrong. It is a fact 
a stock  power cord sounds flat compared a well tuned audio system can pick up changes in any audio cables,that’s a fact.
Relax. When someone says they can't hear any difference you should take them at their word. Odds are they can't.

Their problem. Not yours.
"...the Luxman 505 mk2 which is a class A design..."

Is it?
Good point ,we all hear slightly different and like certain character traits.
Ron over at New Record Day always mentions the cables he’s using in online reviews.
It’s amazing that Ron can differentiate anything as he continues to have a thick, no doubt lumpy, couch for his listening seat.

"...the Luxman 505 mk2 which is a class A design"

Is this really that way? Luxman's website does not mention it, but it does mention class A for some other models. I was under the impression that 505 (I, II) is AB. Where did you find this class A designation?
The 505 is AB, the 550 is A.

Thank you, Luxman, for having a model nomenclature that is super clear and impossible to muddle.

To make it even more clear, I have read insinuations that Luxman’s AB amplifiers work in A until certain wattage and only then switch to AB. It has been floated on the Internet, but no word about it in anything more official/reliable.
I'm no expert, but don't most quality AB amps start off in class A, even if it's only, say, for the first watt (no pun intended), and then transition into AB?
AB amps that attract more attention are those that run quite high into class A before changing over--e.g. some Coda amps.
Class A to class ab they usually have a few watts in class a 
there are Waay to many variables in design  to discount any very well built 
amplifier , 

Ron at  New record day ? He tests things many times what I would not consider fully runin having been in audio over 40 years and owning a Audio store in the past ,knowing all about upgrades,mods, and modding my own Loudspeakers .
digital I give at least 3-350 hours before any serious evaluation ,
amplifiers at least 250 hours for the iron or metals ,and capacitors  need to season or settle in , 
vacuum tube ttransformers can take over 400 , preamps I sold Aesthetixs   and That was unusually long .I was telling people to stop putting their preamp up for sale after 3 weeks ,for the huge power supplies and Bitch Teflon caps ,teflon in general takes hundreds of hours and the Rel caps a solid 400 .
Chris at VH audio tells you his Teflon caps goes through sometimes drastic changes 
up to 500 hours . Just to give you  examples of  extremes .  Also 
to make a comparison to something from memory a year ago impossible,and  many reviewers don’t even use the same cables, and or speakers sourses ,
to me Thst is impossible ,you need to have the same cables speakers to compare whatever it is , that makes sense to be fairly objective.I have read reviews were reviewers used different interconnects or power cords to get the best voicing which I do for my own gear .but if reviewing  if you are going to do That explain how it changed the sonics . That’s why I say read as many reviews as possible before buying anything ,and even if it has a great rating ,you may still have to work at it to get the best synergy in your system. I did a demo with 6 people at a audio get together using  5 different power cords ,it was impressive 
Just how much a quality power cord all different brands,prices can alter the sonic 
perspective ,and soundstaging and detail.