Google doesn't let you post just anything on Google Base; there are certain types of information and items that are prohibited. Most of this is common sense, but here's a short list of what you can't promote on Google Base:
Affiliate sites or products sold through an affiliate marketing relationship
Body parts or human remains
Bulk marketing products, such as email lists and bulk email software
Cable and satellite descramblers and black boxes
Child pornography
Copyright unlocking devices and mod chips
Counterfeit and unauthorized goods
Dialers
Discounted currencies or currency exchanges
Drug test circumvention aids
Duplicate posted content or mirrored sites or products
Fake government IDs and documents
Fireworks
Goods or services that are illegal in your country
Illegal drugs and drug paraphernalia
Illegal knives and weapons
Information on how to create explosive devices
Items and websites that promote violence or advocate violence against a protected group
Manuals, how-to-guides, or other information that enable illegal access to software, servers, or websitesin other words, hacking and cracking materials
Multilevel marketing or pyramid schemes
Nonconsensual adult material
Online casinos, sports books, or bingo games
Prescription drugs (without valid SquareTrade certification, which is available to legitimate pharmacies in the U.S. and Canada)
Prostitution services
Rare, scarce, or valuable metals
Toxic, explosive, flammable, or radioactive materials and substances
Unauthorized copies of copyrighted media and software
Unsubstantiated health cures or remedies
You also can't post on behalf of Google (unless you actually work for Google, that is), or otherwise pass yourself off as a Google employee. Google also prohibits "keyword stuffing," where you include excessive, repetitive, or irrelevant keywords in your listing.
