I think this is something that could easily and inevitably happen everywhere, also, if well done it would also be rather difficult to discover...example: i've always claimed that my engine builder (American Speed of ill...

) is a top notch race engines builder...I could easily post my satisfaction on many chevy forums claiming they're top guys and in exchange get a discount on a new engine..who knows? I mean, i could, but actually i didnt
Another example: Hoosier tires sent me two 4 wheels parcels at the cost of one because the first parcel got, initially, lost, so they've replaced it...hoosier's guy told me i could have the first parcel (free)in case it finally arrived to my home, well it did arrive and now i have 8 tires paid half price. Of course i've repeatedly posted my satisfaction about hoosier client support!! I mean it's all true, BUT could easily be a lie just to create a positive feedback among forum enthusiasts...and nobody would know.
What i mean is that, who knows?, all forums could be plagued by pseudo 'positive feedbacks' but really they could all be just undercover advertisements!

...and maybe there could be crowds of fake enthusiasts posting in forums paid by companies that trade/build products for the motoring market