For selling a product, off the top of my head we've got eBay, Craigslist, Facebook marketplace, nextdoor, and whatever other social network you can think of. Amazon, with a bit of work. Crowdfunding sites if you wanna go that route. If that thing you're selling is a car there's specialized websites for that (shift, for example).

I have only ever been able to have Comcast, ever. In the 9 houses in 6 different cities in 3 different states I've lived, always Comcast was the only option.