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Analyse your traffic to see the words that are being used to find you. Broad match is exactly that, broad.
If your adverts include the first 4 letters of your username then you may be surprised to hear that Google may deem the manufacturer on its own to be close enough to be a broad match!
You can check this by doing a synonym check:
Any highlighted words in the results are synonyms according to Google.
Go through the searches that have been used to find your site and start creating a list of negative keywords such as any other products that the manufacturer makes (possibly with more wheels ;). Whilst doing this you should try to identify the terms that are specific to the subject in question, adding phrases that make sense with those keywords in may help.
A good list of 2 or 3 word phrases on broad match with a nice set of negative keywords may make a huge difference.
Bidding on single words (if you do) is a recipe for disaster.
It seems the OP has tried a little arbitrage without studying the system first. If it was so easy to make money on adWords/adSense arbitrage, we would all be rich.. ;-)