Any question answered...

Not sure if I should be asking this here or in the mechanics thread but here it goes. I just bought this carbon wheel...

...What do you think it could be? No visible cracking or anything like that there, doesn't appear to be fragile. Could a tyre lever do this? Or a blow out? Should I be sending this back to the seller?

I was watching this wheel too. The earlier DT Swiss carbon clinchers were known to delaminate under the heat of prolonged heavy braking, which would manifest in a similar way to what you've described. Naughty seller, methinks.
I'm sure either Dammit or I (or me, Schick) would take the carbon specific pads off your hands if you wanted to offload them. Not all is lost, don't worry :)