I didn't see this interview, but in the past Parker has mentioned this
issue specifically in the context of Bordeaux. He felt many of the
Bordeaux writers of the times (70s & early 80s) derived more of their
income from auction houses and large wine merchants than from writing.
One particular sore point was the tendency of some writers to merely
reinforce the hierarchy-a reluctance to call a first-growth out when it
was underperforming.

A few random thoughts re conflicts of interest:
I personally feel that many merchants can be great sources of info, but
one would be foolish to forget their business is to sell wine.

There is one prominent writer (whose work I usually enjoy) where I have
seen more than one report about the case of Chateau X being put in his
trunk as he is tasting. If true, does that mean he's corrupt? No, but
one wonders if he can totally separate this "generosity" from what he's
tasting.

One should never forget- whether reading a wine magazine, a newspaper,
a newsgroup posting, or an advertising flyer- the old adage to
"consider the source." We all have our biases, prejudices, and agenda
(conscious or unconscious). This includes Parker- but I do give him
credit for trying to reduce conflicts of interest.