If you're an experienced professional or should you have experience in a specific field, you then don't want to register with any old recruitment agency, you intend to find one which will develop the sort of positions that you would be interested in, or else the only jobs you could be offered may simply be inappropriate for your skills and experience.
There are a huge selection of specialist agencies on the market, most of which can be found on the internet. So if you are a marketing guru, someone who is skilled in one of the many areas of construction, or you're a chef etc then don't get a recruitment agency that does 'everything' you will need one that specialises in your field.
Basically homing in your search when on the web, should allow you to locate the right sort of agency. If Inspire Selection enter recruitment agency, you should have literally thousands of options to search through, but in the event that you enter 'Construction Recruitment Agency' then this can start to narrow your options down.
Basically though, some of the search engine results will have 'keywords' mounted on them, meaning that if the Webmaster for a niche site tags the website to be flagged up if 'construction' is typed in, then regardless of whether or no construction jobs are on the site, the website will be high up in the search engine results, so the more specific you could be when searching, then your better it is, so if you want a construction agency that could offer you a job as a Quantity Surveyor or somebody who draws plans using CAD, then type in Quantity Surveyor or CAD designer as well recruitment agency which will soon start to narrow down the search engine. Therefore the more specific you can be, the better!