What should be mandatory in every professional published review-

Honest comparisons against speakers, amps, preamps, of similar caliber is my answer. Previous version of the same brand previous model or other brands of similar perceived quality. 

This would be almost impossible to implement. Most equipment is loaned by the manufacturer. The reviewer won't have a component from two years ago, sitting around. The manufacturer won't be interested in shipping old product out for review. Nice idea, but unlikely.

Thanks,

aldnorab

Telling people what they have to write doen't ring true with me.

An unintended consequence of the internet is that people have figured out how to use it to poison competitors and pump up their own equipment, often in the form of "reviews".  

Unfortuntely readers are often not smart enough to figure this out.

Jerry

Not Mandatory....but....some things I would like to see because they would be helpful to potential buyers:

1.  Take your own photos...top, bottom and back...and obviously the front and if it is speakers, grill on and grill off...why the bottom...I might care about the feet or the holes, or anything else that can be seen.

2.  If its an amp, then use you IR gun and shoot the amp in a bunch of locations...how hot does it get near the bottom, side, back...maybe I'm using a somewhat closed in cabinet and I care if it reads 95 degrees on the top but 120 on the bottom left.

3.  Show me another photo or two of the packaging.

4.  And if the article/review doesn't have room for the photos, no problem, post them elsewhere and give me a linkl

5. What are the problems that might bug someone...does it click, or pop, or hum or anything on start up or shut down?

6.  The sound...the more comparisons the better....and don't just use "audiophile" music....use some stuff that people actually listen to beside audiophile music.

7.  Say a few words about your own bias...what do you like, what do you not like.

"Mandatory" was not the best word to use.  Short of plagiarism, libel, slander and the like, reviewers are free to write in any fashion they wish. If they write in a manner that readers like, they'll be rewarded with a devoted following and continued work.  If their work is meaningless to the majority of readers, they'll find themselves looking for a different line of work. And, lots of reviewers are in the middle, with some readers loving their work, other not, and a healthy contingent in the middle who are "OK" but maybe not thrilled. 

If one is a long time reader of a magazine, you'll have your own mental list of reviewers to which you pay close attention and others which you ignore or discount.  And, that's not to say the ones you like shouldn't be open to suggestions to improve, though as several have noted above in this thread, sometimes practicalities get in the way. How often, for example, does the reviewer have the prior model sitting side-by-side with the new one under review?  If not, that means that any comparison would be from memory, and probably have been in a system with completely different companion components.  Such a comparison would make for interesting banter, but hardly a solid reference point.