Someone created an application that does something resembling an application I'm working on. He claims that his application has a pending patent, but does not mention the patent application number. Searching his name on the USPTO website yields no results. How do I know whether or not he really has a pending patent?
There isn't a reliable way to find this out other than the person sending you a copy of their filing receipt. The default is that non-provisional patent applications publish 18 months after the earliest filing/priority date. During that time the application is not publically visible. An applicant can request non-publication at the time of filing if they assert they have no plans to file out of the U.S. In that case, the first time it is visible is the day it issues as a granted patent, if ever.
They may have filed a provisional patent application. They do not publish at all and give the applicant 12 months to file a non-provisonal application.
I believe there is a way to petition the USPTO to allow you to read an application that the applicant is specifically threatening you with. As I remember, you need to know the application number and filing date.