i had the same problem, but i didn't listen to the people on the forum lol !!
i bought an upgrade kit for my fronts, they were ****, got the seller to send me some new discs and pads for the front and rear instead, never sent the upgrade kit back though lol
firstly he didn't do my wheel nuts up tight enough, which resulted in the wheel nearly coming off, secondly he lied about the callipers and their stopping power, thirdly his brackets bowed
lucky to be alive really !! and he had the cheek to tell me he was getting his solictor involved about me not sending them back, after he LIED TO ME AND NEARLY GOT ME KILLED !!!!