The world of SEO has certainly taken a downturn since every man and his dog began offering link building. You have to sort through the crap to find the good stuff that is worth your while but what really gets my goat is when people constantly say their gig or link package is full of 'quality links'.
Usually these are forum profiles, scrapebox blasts, blog comments, social bookmarks, wikis or web 2.0 sites full of spun content.
Let's be clear, those are SHIT links. Don't kid yourself, they really are. A few years ago you may have got some benefit from them, but not these days.
Anything that is cheap or easy to buy is a crap link. Good links are things like guest posts on relevant blogs which have a decent amount of traffic, links on authority websites and if you have time, manual comments on related blogs that will send you traffic.
Since the last updates link velocity plays a large part. A normal site should only get a few links per day, unless you are a big website with tons of traffic already. So if you go getting 1k wikis pointing to your site in a day or two, Google will spot this a mile away and either knock your rankings or ignore the links, thus meaning you are wasting money.
Spun content is now another thing they can pick up on. Don't do it! Write articles yourself or outsource. You will get much better results this way and in the long run the posts will stick. Google can detect when an article doesn't make sense. Worryingly, their technology will only get better too.
BEFORE you go buying link packages you MUST make sure your website is optimized as much as possible with good interlinking structure, META titles and description, and has been checked for conversions. You can get thousands of hits to your website but if it doesn't convert them into sales you are wasting your time.
I hope this helps, especially people new to the game. I hate to see people buying 'quality backlinks' when I know from experience they are absolutely worthless. If you sell these yourself, just think about toning it down a bit and being realistic to your customers. Karma can be a good thing.
Rant over