Hi Patty, my first job on Elance was blog commenting. The truth is even though I tried my best to do a great and genuine job of reading all the articles I was posting on, the client still got banned by Akismet.
During one of my communique with the client I pointed out that I came across several blogs with their signature posted more than once. I also pointed out that each post was different and seemed like spam. What the client did not get was that if you hire someone to post a comment on a blog you must point out to them that they should look through previous comments to make sure they aren't commenting again unless it's an ongoing conversation they are contributing to. The client should also point out to the contractor that they need to read the blog posts before commenting and make relevant posts to the content (much like on HP).
I will recommend blog commenting be done by the owner of the URL you are promoting and not a person you pay to do it. Good blog commenting pots are not easy to spot but if you see the same person posting on the same blog twice, you can be sure it's a paid comment?