I presume you mean this part:
“If you are discussing other subjects in the channel, other players on your realm can consider those unwanted messages as spam. They may report it as such and therefore the penalties associated with spam may be applied to the person reported.”
In the end, it is up to Blizzard to determine if what is reported truly is “spam”.
As examples:
Example A
Johnny and Billy are having a conversation in /trade. Neither one is repeatedly posting any message. Every one of their messages are different.
Bobby gets his friends to report Johnny and Billy for “spam” in order to squelch them. Blizzard overturns those squelches, reinforcing their policy that speaking about non-Trade subjects in the Trade channel does not violate their chat policies .
Now, Bobby and friends abused the system and reported Billy and Johnny with the intent to squelch them, but how does Blizzard prove that the system was abused when “spam” is a “valid reason” for submitting a report? How likely are they to punish Bobby and his friends when they cannot prove that Bobby and his friends abused the system?
Example B
Johnny is repeatedly posting the same LFG message in /trade once every 4 minutes.
Bobby gets his friends to report Billy for “spam” in order to squelch him.
Blizzard overturns that squelch.
Once again, Bobby and friends abused the system and reported Johnny with the intent to squelch them, but how does Blizzard prove that the system was abused when “spam” is a “valid reason” for submitting a report? How likely are they to punish Bobby and his friends when they cannot prove that Bobby and his friends abused the system?
Example C
Johnny is repeatedly posting the same LFG message in /trade once every 30 seconds.
Bobby gets his friends to report Billy for “spam” in order to squelch him.
Blizzard reviews and determines that Johnny was at least pushing the envelope of “spamming”. They take what they feel is appropriate action.
I like how you chose to focus on the portion of that second post that mentioned “spam” while completely ignoring the first post:
"Spam is in the eye of the beholder.
My personal level of tolerance when playing - if you are doing it often enough that I start to get annoyed, yeah - you are going to get reported.
People tend to not like advertising very much, and you’ve not mentioned what you are advertising. Not only do you run the chance of getting silenced, you are alienating potential ‘customers’. I’m making a very large presumption here that whatever you are advertising is indeed within the rules."
That would be the post which seems to me to address all chat (including the use of /trade for the selling and buying of goods or services) and also includes the following sentences:
“People tend to not like advertising very much”
and
"Not only do you run the chance of getting silenced, you are alienating potential ‘customers’ "