We were one of those newbies, we where giving out more than we where earing and got too expensive to keep up, but it really is trial and error, we researched it and use it every now and again but never for too long and is very targeted.
That is a very good point. Never trust a company that promises a guaranteed top spot or amount of traffic. Google is an unknown quantity and you can estimate based on previous traffic but you can never guarantee anything with search engines.
Some websites now offer guest blog spots where you can feature articles you write, this can help gain good targeted traffic as most allow a link to your site as credit for the piece.
There are also many free ways that businesses might advertise there business FREE
create business profile on google and create a google map listing
free yell.com entry
free bt trade entry
advertise services on ebay free
craigslist
gumtree
touchlocal
Whatever you do avoid a company called dotcomchrome who are a google adword reseller