Very good question by OP. Googling
SEO services is useless; there is no way of knowing who does things right, abiding by webmaster guidelines etc.
And regardless of claims to the contrary, black hats do dominate a lot of SERPs in Google. Just goes to show that questionable methods, unfortunately, pay off.
On the other hand, bad
SEO / blackhat
SEO can seriously backfire, so if you end up hiring someone who does it wrong, a lot of damage can happen.
I'd be very interested to hear first-hand experiences/results, recommendations for a good
SEO firm.
Obviously, the best
SEO is quality content. If you have good enough content (read: incredibly good content), that's all the
SEO you need. But for many purposes, professional
SEO can help.
Anyone confident in their abilities, shoot me a PM, I have a lot of projects that need some
SEO done.