I have both, a genuine Dyneema rope that I bought from the US, cost a bloody fortune , and a Ebay Dyneema rope .
I have used both of these rope in many recoveries, but, I have managed to break the genuine rope once, never broken the Ebay rope.
The ropes when new looked the same, ( both were 10mm ) but the genuine rope was softer where as the Ebay rope was stiffer.
cheers duggie