The biggest signal of someone being an amateur when speaking (or writing) is discussion of the process of creating the presentation. Polished professional speakers don't talk about "when I started writing working on this presentation, I wasn't sure how to talk about X." They just put together a presentation describing the result or topic and present it without talking about all the work that it took to create. The process of creating it seems very salient and novel to the creator at the time of creation, but the audience doesn't care.

People who are nervous or give public talks only rarely will regularly fall into this trap. I think it's related to self-handicapping in presentations, but is distinct, and I have not seen it mentioned in looking at a few "presentation pitfalls" articles.