Wow, this is an interesting article! A little bit personal between monkey and smasher but very interesting to me as I was actually searching for poor quality Blanco sinks! The reason being I had a very similar problem which after much arguing and investigation turned out to be my builder at fault not the sink. So I understand why monkey must feel aggrieved but the sink isn't at fault here. Once you got my attention I couldn't believe the similarities although not exactly the same but not far off.
You see I left my builders alone to finish the kitchen and came back to a similar looking sink, long story short, the culprit was a metal bucket and builders sand! As the builders generally use anywhere to store things, let's be honest there's our level of tidy and then there's building site tidy (miles apart) now for the technical bit the sharp sand over time, I was away for just over a week, will react with the steel as will certain metal objects the sand reaction depends on the salt content and the metal reaction is what they call galvanic (I had to Google it) and it certainly looks as if you've suffered something very similar cheeky monkey.
You see a bucket of clean water as you say would not cause that level of pitting rust in only 24 hrs as you suggest, to do that the steel would have to be nearly pure iron. Also looking at your pics the rusting would concentrate where the water would collect e.g. around the waste, in the corners/edges and in the drainage channels. But in your pics there is little or no rust in those areas. This would suggest a liquid suspension could be the cause, for example when you clean plastering tools the splashes of dirty water would not drain out if not flushed so they would collect in spots and over time could react. Any metal tools stored in that sink even over a weekend could begin to rust and in turn damage the sink. The levels of tarnish around the rust spots actually points towards galvanic reaction of dissimilar metals, so that could be the cause perhaps, especially as one photo shows a number of vertical lines on the vertical side of the sink and we all know that, thanks to gravity, clean water does not stay vertical very long .
Like I said I'm just trying to add a rational rather than emotional explanation from experience, you said yourself the second sink was fine, a bad batch of steel would more likely affect the whole stock not just one sink as these are bulk purchased and to give some credit to smasher, stainless steel is not a surface finish like powder coating, enamel or chrome is throughout the entire sink, so cleaning it probably would have done the trick, Blanco did mine it came up like new and meant I didn't have to rip apart the build to replace the sink.
Did you witness the water test and return the next day? Coz methinks someone might be telling you porkies to conver their guilty behind. In my opinion of course I can't speak for customer service but it does look like 1810 didn't sell you a dud sink. I'm certainly going to give them a go and ill report back here if I find any problems and if smasher helps sort it or not.