This should be in Internet.
Yes, it works if you do it right, but don't expect to pay someone small amounts of money and then wonder why nothing is happening, or why they've attempted blackhat strategies. Also, don't expect things to take place over night. It's a long process and often an on going one. I've got 3 keyword searches with 120m results to #1, only for the owner of the website not to continue updating and find them vanished just as quick as we got them there.
I've also made minor changes to websites, for their hits to double in only a few weeks, along with their contact rate, but it will depend on many, many factors. Don't invest into people who guarantee you a #1 spot, as everyone would be there otherwise. Although many firms work on a bonus scheme, where if they get you to where you want, you pay them a specific bonus (normally a large chuck of dosh, but you should have made that money back x times over by that stage). Also, remember the most generic terms are not always, and are often not, the best.