Regarding bumping ads in the classifed forums, we've just installed a new (customized) add-on that will change the way ads are bumped to the top. Please refer to the post "Bumping Classifed Ads" for details.
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These ads go away when you register for an account!
Say, hypothetically you had four items and bump continuously, you are putting every new item four in the hole. Interested parties know the items are available, they just don't want it at the price it is being offered.
I'd also say no advertising your parts on other people's posts. I was trying to sell a part and some idiot came on and told the guy he had one on my post and tried to sell it without making his own thread.