Every eCommerce business owner should strive to have good SEO: make sure that your website is well designed, is full of well written content and is easy for customers to use. All of those qualities are things which Google values highly and, as such, they will rank sites which have those qualities on the front page of search results. But SEO isn't just about having a good site, another enormous factor is how many links back to your site you have and this is something which can have a very negative effect, if done badly.
One thing which you always need to remember is that good SEO shouldn't look like SEO at all. Google will penalise sites and remove them from search results (which can lose people thousands of pounds) if they find that they have been taking steps to artificial manipulate search engine results. If you find a website that has "SEO" in its name and is promising to improve rankings, this is definitely something to avoid because that is clearly an artificial attempt to manipulate rankings and Google could penalise you for it (and will doubtlessly penalise the SEO site too.) If you're trying to increase the number of links leading back to your site, it needs to be done in a way that looks natural and if you do have a good site, the chances of gaining natural links is much larger!
You need to remember that Google can see everything - if you pay a spammy business to put your link on a thousand random sites, Google will easily spot that this was not authentic and potentially take action. Take it slow, keep it natural and focus on the quality of your site and everything you put out into the internet and you are much more likely to feel the good effects than if you resorted to some bad SEO tactics. Hopefully this advice is useful and you will be able to continue to enjoy success on your eCommerce website!