No link is provided so we'll have to discuss without a look. If you don't want SEs to find this thread, give it to us like mydomainDOTcom or mydomain dot com.
You'll find that many of us on the forum think that SEO stands for Someone Else prOfits.
If your product is too unique (if no one is searching for it), nothing you can do will help. If you're the only one making frabbingdingers and no one knows what one does, no one is going to look.
If, as you say, the knowledgeable Google searches are coming back in the top ten, you're best option is to beef up content. That's what Google rewards the most. In fact, doing most of the things an SEO "expert" would suggest just might hurt the top ten more than help.
You might want to throw some comparisons into your descriptions bringing similar products into play. If the dobbingdinger is similar to the frabbingdinger but does not provide features 1, 2, or 3 that the frabbingdinger does, put it in the description. Then, if someone searches for the dobbingdinger, your site might be listed as well.
Last thing you need to do is mess with Zen Cart's URLs. Google and other SEs have no problem reading the info and changing now would mean you would have to wait months while the SEs try to sort out what you've done. It's no coincidence that the URL rewrite forum threads have thousands of horror stories posted. Don't mess with what works.
Also, don't think that stuffing keywords or fattening descriptions will help. Saying that "Our frabbingdinger is the best frabbingdinger you will find of all the frabbingdingers on the frabbingdinger market today." will drop your rank like a rock.
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