Doesn't look like cracks to me. I'd save sanding this and just send the frame back if you can, on the basis that it was not received as described since it has been damaged to the point where it is unsafe to ride.
@rodabod started
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Doesn't look like cracks to me. I'd save sanding this and just send the frame back if you can, on the basis that it was not received as described since it has been damaged to the point where it is unsafe to ride.