? Offers to do a lot of search engine submissions for you. These will do absolutely nothing for you. Nada. Zip. Let the search engines discover you through links.

? Recommends 302 redirects. I saw this just this past week. A major SEO firm that was helping a client with a move from domain to another, and they recommended 302 redirects. No faster way to destroy all the historical trust built up in a domain.

? Focuses on link swapping. This is OK, up to a point, but it is not the fundamental building block of a long term link building strategy.

? Uses the same link building methods on all clients. If it sounds like the link building strategy is the same for all their clients, you need someone else to oversee your overall link building strategy. Note that working with specialists is an OK thing to do (e.g. someone that focuses on social media), just don't let that be the only thing you do.

? Recommends micro sites as a way to rank for more terms. Unless you have been penalized, you are almost always better off putting new content on the existing domain. Every time you create a new site, you have created a new thing that you have to go market to get links for. Much easier to keep it all in one place.

? Recommends that you run your content across multiple domains. I saw this recently. A company was doing a site move, and their SEO firm recommended that they keep the old domain running, then create the new domain, and leave them both running for 6 months. Not going to work.

? Talks about hidden text (or other tricks such as cloaking) as a strategy. If it feels like a trick, then it's probably a bad idea.

? Says they know the Google algorithm. Hell, Matt Cutts doesn't know the (entire) Google algorithm. Sure, he knows more about it than anyone outside of Google does, but the Google algorithm is really a large morass of different algorithms, and no one person knows all of them in intimate detail. In any event, even if a single individual inside Google knew the entire set of algorithms, they won't be sharing that information with an outside SEO firm.

? Promises #1 rankings. An old favorite. No one can guarantee #1 rankings, unless you are talking about "left handed oil based bottle washer". Face it. Your space is probably competitive, and there are lots of people who want to rank #1 for the most important terms, and they are all trying to do it. Good SEO firms will bring you good results, and help you grow your business. Basically, it's the wrong metric. How big is your web based business today, and how much can the SEO firm help you grow it? That should be the focus.

? Don't want to let you know what they are doing. If you get one of these, it means one of two things are happening: (1) they are doing nothing, or: (2) they are doing something bad.

So as I said before, there are good SEOs out there, in fact, there are lots of them. They can really help you. Unfortunately, a bad SEO firm can really, really hurt your web site and it's traffic from search engines. Learn what to avoid. In addition, learn what to look for on the positive side. A good start on that task is to find SEO firms that will start be educating you on the challenges you face, and then focuses on the nuts and bolts about how you meet those challenges.