One good quarter of comparable-store sales growth didn't shake the conviction of Michael Pachter, a senior analyst with Wedbush Securities of Los Angeles and a holdout among securities analysts who post a recommendation on Best Buy Co.'s stock.

According to Thomson Reuters, of the 27 investment recommendations published about Best Buy's stock on Friday, 17 were a buy or strong buy rating. There was precisely one sell recommendation.

That's got to be from Pachter, who actually has an "underperform" rating with a 12-month target price of $18 per share. If he's right, that would be quite a painful ride down for shareholders, given the current share price of more than $38.

Pachter, in an update report published Thursday after Richfield-based Best Buy released its quarterly results, once again makes a very good case for skepticism. If his were the only research report a shareholder ever read, that investor just might sell.

It is important to note that he is not critical of the people running the company. To the contrary, he's somewhere between fair and generous in his comments.

In his latest update he apologizes even, for not only having been wrong in his comments in a TV appearance about the iPhone 6's impact on revenue growth, but also saying Best Buy was disingenuous.

After seeing this CNBC segment, I would maybe suggest he think also about following up with a handwritten apology note. And maybe flowers.

The point he makes in his far more measured research report is that the challenges are beyond the talents of anybody trying to run Best Buy.

It's hard to summarize his lengthy analysis, but perhaps the simplest way to sum up his views is that Best Buy is doing a good job of improving the experience of customers who come into a store, but it just can't seem to get any new customers.

Further, having to match prices will mean more very painful margin contraction. Finally, the company's online efforts are just too late.

He wrote that one of the biggest mistakes of his career was thinking that Blockbuster was going to be able to build a competitive online business to go head-to-head with Netflix. After $1 billion of cost and Blockbuster's bankruptcy, he concluded that any traditional retailer trying to catch up with an online competitor faces very long odds.

Pachter may one day be proven spectacularly wrong about Best Buy, yet his position is actually an easy one to respect.

If one quarter of stronger-than-expected revenue growth was enough to collapse his convictions that Best Buy remains vulnerable, then he wouldn't be an analyst worth following.