Interesting... patents are something I'd never attempt to file on my own, if I were worried about enforcement (rather than simply "owning IP" for acquisition or investment purposes, which is usually why I bother). In a patent case, the scope of your claims can really come back to bite you.
I'm still trying to figure out how someone can screw up a domestic trademark application in a way that's both serious and non-obvious, however. If your mark is too close to another, USPTO will simply reject your application and you'll be out a few months and the filing fee. If you register in the wrong class, simply file in the correct class. IIRC, the application only asks for the mark (which for many is simply a wordmark covering the term one wishes to trademark), the classes you wish to register in, a specimen, the dates first used and first used in commerce, and your contact information. Where in that information is the potential for a subtle screwup?
I'm not doubting anyone and certainly have less experience than anyone who does this for a living, but I'm genuinely trying to understand where the landmines are.