Yes been looking over those forums and doing my research on those suppliers through them.No comment on your logic, just a suggestion that you may want to check out the forums at endless-sphere.com. It's a site devoted to electric vehicles that caters to DIYers; they could definitely help with finding a reputable vendor for batteries and/or steer you away from questionable vendors. I've been lurking there for a while researching motors and come across a smattering of related discussions on batteries including suppliers and build discussions.
If you don't want to do a lot of reading you could do a search on each vendor you're considering and see what comes up to help you decide. Doing a quick search on "batteryhookup" gives 122 matches including multiple hits from amberwolf, who some members on this forum may remember. And searching on "GVW" gives 51 matches but most of them appear to be in context of "gross vehicle weight".
I am now fairly set on the K2 26650 cells from BatteryHookup. The only thing I am wary of is the duties I will face, in theory they should just by 3% duty and 23% VAT and €15.00 Fedex handling fees - but I can find no absolute clarity on this so I could get a nasty surprise.