I have to say, the reviews I have done supported by the manufacturers, JConcepts, XFactory etc. They have just been happy to have a review on my site and never mentioned anything.
Needless to say, even if I buy a car myself, it is useful to get technical help or advice / interviews with the companys. But generally, if they don't want to help with a car they will not help in any other way either, thats true in 100% of cases so far.
I can give examples of companys that have asked me to give favourable reviews, but there are none of those companies products reviewed on this website
