I was checking out a deal on an iPhone and ran into this scam. I got the same format style of email and was suspicious. Note that scammers can take it a step further to hide the fact it is bidcactus and/or to track their "scam-ees" - I was told to go to retailbidday.com not bidcactus.com and (as a web consultant) I watched the URL activity and retailbidday.com immediately redirected to bidcactus.com. That was when I was pretty sure it was a scam (although that is not always true). BTW, I am sure there are a whole lot of other URLs that people have bought to propagate this scam so if you get a different URL like I did please share it.
Here is the content of the email sent to me after responding to the ad on Craigslist:
"Hi Someone just purched this from me, but I can tell you where I got it from. I just got 4 of these from here retailbidday.com and I resold them for some extra money. The trick is to watch for bidding to slow down and then jump in. That's what I do and I win all the time."
Also note that they appear to be a sort or real penny auction site and somebody had mentioned they were rated B+ on the BBB website. I checked that out - they have a D+ rating and are not accredited with several unresolved complaints on file. The BBB rating report: http://www.bbb.org/connecticut/business-reviews/penny-auctions/bidcactus-in-westport-ct-*******
BTW, I suggest if you run across one of these craigslist scams that you take the time to go back and FLAG the listing to have it removed. These postings are prohibited and you can just click the link at the top of the craigslist page where the post is located to have it flagged for removal.