Look, some people might say; "Why give a talk on detecting, that's stupid. You're also getting more people (competition) into the hobby". However...
I'm not so sure that rationale works very well. Why? First...
Let's face it, we're under the gun a lot. The unwanted attention from these dumb MD'ing shows, the false assumptions of a paranoid public, the Gestapo-like tactics of beuracrats who despise detectorists, etc. So...
IMO, having these friendly talks helps
educate folks on who we are & what we do. Second...
It would establish you as an instant expert in your niche. You start being known around town as 'that metal detecting guy', and the word spreads. You might get calls from the local police department to help detect a crime scene, you'll start receiving calls to find valuables people lost, etc. A terrific source of never-ending leads
And one wouldn't necessarily need to be the best speaker, or have a long presentation, or mind blowing finds, either. Heck, we're talking about having these presentations in libraries & similar locales. Simply hit Wikipedia up and come up with a bullet point on the history of an area. Then, open your talk with that. Next, explain you're a detectorist, what that is & why you do it. You might then segue into some of the 'fascinating historical finds & artifacts' you've found in your travels (hey, isn't a barber dime historical?! Lol). You can pass the finds around for all to see, then, towards the end, you can have a nice Q & A session. Also...
Make sure to pass around, or have a clipboard available, where the guests can
sign-up to get follow-up information on how to get started in metal detecting, what detector to buy, additional history on their town, yadda, yadda, yadda. This list would be a treasure trove. The metal detecting expert (you), helping people out & entertaining them. Ya think you'd be given permission to hunt their properties if you emailed them?
Finally...
Again, any chance to help educate the public on what it is we do, and to take that negative stigma away, is a good thing. And having some fun & BS'ing about detecting ain't all that bad, either
Joe