Another thing to consider regarding Dexter and the used car salesman. The plot is developing that all of the victims were either ex-convicts or suspected in a crime. This does not hold true for the salesman. The victims had semen samples collected that there were no DNA matches for in the PD databases. This would confirm both that he had no record, and that he also was not a suspect, or they would have ordered a collection for a match. This victim should be soon rushing along with the current to the mid atlantic, never to be seen again. Therefore no connection could be made to Dexter.
I, however, like you guys, felt it weird that he made any connection on paper, whatsoever, with any potential victim. The only way he could be linked to this crime would be through correlations after he was made a suspect in the others, not before, in my opinion.
Best episode of the season for me, and by far my favorite show on TV.