Auction properties come with additional risk, and many buyers don't adequately discount the price for the risks, time, money, etc. that they're taking on by buying such properties. However, since many of them are listed in the MLS, they have every right to advertise on sites like Trulia.
As an agent, I generally will advise my buyers to avoid them. Unless you get a really great deal (like 30% below market rates) it's just not worth it.