SEO Services on ebay or SNS
I've used SNS for some seo services, for that it is fine. One guy on there did an analysis of a local site for me and sent a report with recommendations. That worked out OK too.
I would stay away from the SEO stuff, for the most part.
I never did much with SEO services on my main site. I built my traffic slowly and over time. I included a flyer with a coupon with each eBay and Amazon order. It does not cost much and a certain percentage of people will turn into regular buyers. I have started to use, thanks to Aspkin's advice, Adwords which are highly targeted and so far, so good. My site does about $6,000 per month in gross sales (NOT PROFITS) and that is not bad.
I think it makes more sense for most people to stop thinking in terms of keywords, articles, links and other such things and START thinking about their Return on Investment (ROI) on paid advertising. That could be including a flyer with your eBay orders, Google Adwords, an affiliate program, or other things like that.
Years ago, you probably COULD hire an expert and get on the first page of Google. You could also BUY your way in to Yahoo. Those days are over, the web is too big now.
When you think of all the SEO going on, and the fact that there are what - 20 results on a Google page?