You're trying to find a technical solution to a people problem. That generally doesn't work.
Finding a people solution will yield better results: stretch targets; output quality reviews; regular 1-2-1s; discussion about career progression; more responsibility.
If they're actually at a low enough level where a program will obviate the need for you to fulfil your managerial responsibilities, why not outsource, pay for piece work, etc. There's no benefit to you to keep motivated workers employed - there's nothing to motivate them /with/.
No SEO can guarantee results. They aren't the search engine, so how could they?
I'd be interested in the changes to your site, your data architecture and your content that they have suggested because, if that's not how they've worked, you've at best (or worst) engaged a bunch of black hat SEOs whose actions may cause you extreme pain down the line. At worst (or best, depending) you've engaged people who have taken your money for no action, but at least there's no reputational damage.
If you /have/ had proper engagement from the firm, you will probably have derived value from their work in the areas I mentioned above, regardless of your SERPS position.
Per-block dedupe, I bet, so it'll get benefits at sub-file levels.
Though given that the vast majority (by volume) of customer data will be people's illegal downloads, their scheme effectively reduces to being a copy of usenet.
I suggest you stay away from any of the elance/rentAcoder type sites, even if some of their customers seem to offer the skills you want at a price you find acceptable.
I gave them a try a couple of years ago to earn some beer money (I'm a sysadmin), and the rates that people went for were /so/ damn low that I literally couldn't see the point and just negotiated a raise instead :-)
I somehow doubt the genuine expertise and experience you'll derive most value from during a couple of hours session /won't/ be found at those low, low rates. Sysadmin are expensive ;-)
I see that you are based in London. I'm guessing that's why your rates are much higher than the Elance crowd. There you'll find lots of sysadmins in India/Russia with rates from $5-10/hour. There's no way you or I could (or would want to) compete with that (I'm based in Los Angeles, US). I wouldn't doubt their expertise just because of the low rate...it's just that the cost of living is much lower there. That said, wherever you find someone, you would want to do a certain amount of vetting before you give them access to your server and network, and once you invest the time finding someone, you want to keep them around more than a few hours.
