When trying to find an SEO agency it can be very difficult to determine a list of criteria particularly when you don't understand the SEO process. Virtually every SEO consumer would expect a good SEO agency to appear in the the top of major search engines for all their relevant key phrases. Although this concept seems very logical it doesn't necessarily reflect upon the other agencies which aren't. There are literally thousands of SEO companies out there and with a relatively small number of positions on the first page, it's impossible for the agencies to prove their value when you are on the first page. It's only when you begin to break down the current high performing SEO agencies that you start to create a better understanding as to why they are there and most important why you should not use them. There are endless checks you can do on an SEO company but I would strongly urge anyone to use the ones listed below accompanied by deeper checks you think to be suitable.
Search their company name
Searching their company name will inevitably bring up their directory listings, article articles and social networking pages in case your company is relatively large, there will be some feedback somewhere. It's highly likely if someone has had a good or bad experience with an SEO company, they would have mentioned it on a webmaster forum or a blog. It's very important not to take these reviews at face value because some underhand SEO agencies promote their services this way, whether it's a forum look at their post count, join date and response from other forum users. SEO
Look at their collection
If an SEO agency is good at what they do there will be an endless method of getting testimonials, don't be afraid to ask the agency for previous examples of their work. If an SEO company markets a lot of clients yet somehow only displays a collection couple of testimonials, ask them why or even better ask the owners of these websites. Website owners are more inclined to tell you what's not working or has never worked as opposed to what's working well.
Check their back links
A large proportion of online marketing is back linking and there are endless amounts of free tools to check the trunk links of a particular website. The standard of web sites linking to this SEO Company will reflect upon the honourable standard of their work. If you discover an agency to have a vast amount of back links from websites you would consider as being spam it is highly likely this is the approach they will take to marketing your website which is against all major search engine guidelines.
It's very important to know how an SEO company will work on your website, if at some point you think you are being blinded by technical vocabulary or if you feel like the company is not being completely honest it's highly likely the agency is working unethically or in SEO terms using Black Hat SEO. If at any point you get Black Hat SEO I would strongly urge you to leave that SEO company.