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How many links does it have?  anything sub 300 is nothing to be concerned about in my experience.  Google does recognise the need for some sites - particularly large ecommerce sites to have lots of links for navigation.  As a rule of thumb (imo) if it aids natural customer navigation, it's fine.  If its overtly spammy and a deliberate attempt to cury favour in SERPS, its not fine - and apart from anything will ultimately dilute what you're doing by appearing on every page.

I checked a few and the link profiles were ok but not great. I cant help but notice that clicksubmit's own DA is a measly 27 which is odd.

Over all though I cant see anything alarming, so I might give them a go, it's fairly cost effective, and I am tiring of using off shore agencies who promise the earth and deliver either nothing or very dangerous work.
In an ideal world I could add 10 hours to the day so I could build links myself!

i take it ecwid doesnt support the native joomla friendly urls?  are friendly urls and rewrite even switched on in the joomla core config page?