just selective benchmarks (which both vendors do) and marketing statements like CRUSHING COMPETITION, and "poor volta" giving a pre release impression that there cards will perform better then they ended up doing
There are stacks of thigns AMD have done such as withholding driver updates to the 290x and saving them for the 290 re-brand which AMD insisted was not a re-brand, and blocked the driver form installing on ot the 290s. Only some people hacked the 290 firmware onto the 290 and managed to install the new drivers and magically got the exact same performance, thus forcing AMD to open op the driver updates to the 290 series, of course only after all the reviews were done.