When reviewing the recent answer here, I down voted the answer and left a comment. After that I lost a reputation point. I'm still learning all the dos and don'ts of the stack exchange but the only options I had for the "First Posts" review is to down vote or comment, and after the down vote a comment is requested. What is the proper way to review something like this or did something else happen to cause the loss of a point?
There is a general discussion of downvoting and the rep lose in Why do you lose reputation for down-voting?.
Basically, there has to be some repercussion for downvoting or users could abuse the feature.
A comment is a good starting point. If you feel strongly that that an answer is wrong, downvote it. Downvoting without a comment is bad form IMHO. You aren't giving the answerer any opportunity to respond to the criticism or modify the answer accordingly.
Of course, that is just a suggestion. You are free to vote as you see fit.