I used to sell on Craigslist but I started to get nervous about strangers coming to the house as well. I've had luck selling some stuff on Facebook though local DJ groups, but most of my sales have been going through ebay. If you you do sell on ebay be sure to get insurance on anything you sell. I recently sold a 2016 Macbook Pro and the Post Office lost it. I had insurance but not enough. The insurance that they initially offer you is not US Postal insurance but rather a third party that only will insure up to $1000.

As far as being able to show that your item works properly, you just need to really communicate with the buyer. Send lots of pictures and videos of the item in action. Good luck with your sales and remember to get insurance.

You could always meet at a public place, like a post office or a college or Starbucks. I would never meet at your private residence or workplace.

I sell on craigslist, and complete transaction in parking lot of police station

most police stations actually designate them as "safe transaction" zones. ight be difficult to let people test things out like pa speakers tho...

The problem is having a power supply avail in some public spots.

i have ppl meet me at a gig 1hr before i start or at a public place like a starbucks

Facebook Marketplace. I generally have them come to my house and i show them the gear in my garage. FB marketplace is better than craigslist. generally a great market and you can see who the person is that you are going to sell to. Ive had great luck selling gear on FB.

Facebook is the worst place. Many inquires aren't serious, and they lowball before even coming to look at it...and that's the other problem, no-shows. Waste of time in my opinion.
But I suppose it depends on what you are selling..