US PATENT TRADEMARK OFFICE SEARCH LIMITATIONS
US patent trademark office searches are often conducted like a domain name check because searchers compare trademark registration with domain name registration. They think of searching for a specifically worded trademark and getting an immediate decision on whether or not they will have unquestioned rights to that trademark. They need to understand that this view is erroneous before they can appreciate the limitations of the USPTO search.
There's a night and day difference between domain name registration and trademark or service mark registration. If you complete the trademark registration process in 15 months you're lucky. During that time, and even after registration, your rights may still be contested. This is because the standard as to whether one person is violating another's rights is whether the marks are "confusingly similar" and, if they are, who had first use. The two marks may not be spelled the same, or look precisely the same. Someone has a problem (you or your competitor, whoever is the junior user) if a court would find, with 20/20 hindsight, that the public could be "confused" between the two marks. An example: May Department Stores claimed to spend millions promoting "be" for women's clothing. They filed a trademark application. Bebe, a women's clothing store holding a trademark registered earlier, sued May and won. Try finding "bebe' with a simple search using the word "be" on the USPTO site and, for that matter, try finding the May "be" trademark application on the USPTO site. A thorough professional search could have saved May those millions.
The determination as to whether two marks are confusingly similar is not an easy question. This is why an adequate search should be done before you file. Otherwise, your $325 filing fee with the USPTO (per class) could be an immediate waste of money, not to mention your possible exposure to trademark infringement. The better the search the less likely that you will, at some future date, find yourself embroiled in trademark litigation with the user of a similar mark.
All this being said, it is still true that the free USPTO search is the best starting point.