Agents who "assist" in self-publishing

There's a good post here by Laura Resnick about why agents who "assist" at self-publishing may have a conflict of interest. I totally understand why some people would be willing to give up 15% of their income to have someone handle stuff like covers, editing, and marketing-- some people just do not want to deal with all those details, and prefer to focus on writing. I'm not saying you should never, ever go into such an agreement with an agent, but I do think authors should approach such agreements with extreme caution.