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I would guess its related to your issue "www and the non-www versions of their websites are both in play" meaning that MOZ is crawling them both as separate sites and you will have different links going to the www version than you will the non-www version, which will give you different spam scores. It would be good to compare the link data that MOZ gives you between the two URLS, downloading the CSV of both and having them side by side in one spreadsheet might be easier, this should give you an indication of what links are causing the spam score to be higher. I would also suggest loading both www and non-www versions of your website into Google webmaster tools if you haven't done so already.

Hi Brian,oo problem, happy it helped! Of course- it's always better to confirm with someone else when there's a lot at stake!