USPTO trademark data is free and public. That is exactly the problem.
I have spent the last few weeks working with public government data (before that: SEC filings, which have the same disease). Trademark data from the USPTO — the Trademark Status & Document Retrieval (TSDR) system and the Open Data Portal — is complete, authoritative and free. It is also scattered, rate-limited, XML-heavy, and completely without any notification mechanism. If you have ever needed to know, programmatically:
whether a mark is live, dead, or abandoned (and when that changed),
whether an office action was issued (they carry strict response deadlines),
whether a confusingly similar mark was filed in your class,
