Bests & Worsts Reviews from Amazon

I bought 6 of these plugs for my 2013 BMW X3 35i. My vehicle was running just fine, but I decided that I wanted to do some preventative maintenance, so I installed them. After driving 20 miles, I realized my vehicle had a misfire, which I could feel while waiting at a red light. As I took off, I didn't really feel it again until I got to the next red light, and the misfiring got worse. From there, I headed home, and by the time I got there, my vehicle was in limp mode. My OBD scanner showed failure in cylinder #4, so I pulled the plug out, replaced with an old plug - misfire gone. I put the new plug back in, and the misfire returned. BAD PLUG. So, I stuck with the old plug in #4 and figured I was fine while waiting for a new plug to deliver. I drove about 50 miles from my home, and realized the misfire was back. Unfortunately, I was too far from home to get back, and my vehicle was in full limp mode, so I had to get a tow to the BMW dealer. After 2 days of not having a vehicle, the dealer told me #6 plug was no good and needed to be replaced. I told the mechanic the story, and he recommended replacing all of them with genuine BMW plugs - $1230 after tow, labor, and parts, which I ended up doing, just to avoid being stranded again anytime soon. Ultimately, I think these plugs are maybe fine, but I bought mine from marketplace seller European Parts Haus, and I question whether they were authentic. I spoke with Bosch and was informed that European Parts Haus is not an authorized Bosch dealer on Amazon, so who knows where they got the plugs from and if they're even new. Bosch advised that it's entirely possible that European Parts Haus bought plugs that had been previously returned to Bosch due to defect or dropped product, which causes failure. From there, if they're reselling on Amazon, they're unauthorized to do so, but Amazon doesn't control sellers and what their authorization is. My recommendation is to buy these only from Amazon, not from other sellers on Amazon.