I generally have excellent page rank in Google for my products. Often in the top 5 or 6. However, I have paid nobody to get me there. I rely on well written descriptions using terms that I hope the average shopper would use and good feed.
Makes me chuckle when I get these emails from the SEO dweebs telling me they could improve my page rank for me and only charge $$ per month. What BS those companies are. Do it yourself, you will know your products better and you will have a better feel for how your process operates.
For me the best ways to get good page rank are to have well written descriptions and to submit your feeds to the big engines on a regular basis. Most of them will take your feed for free. I ignore the ones that want money from me for the privilege of them making money off ads.
I use to use a submitter http://www.blastengine.com/ and they were actually pretty reliable and moderately priced. I believe it was $25 a month. And for the first few months I noticed a significant increase in traffic to my site and better sales. After awhile it started to drop off. I found out that many search engines tend to stop accepting submissions from such companies. So I got a list of search engines and went to many of them one by one and set up my own submissions. Many of them are as simple as just submitting your www.homepage.com and they would crawl it.
Now I just focus on the bigger engines.