OK, two ways that work for me on CL.
The first is to search all listings for a particular city. I the screen shot below, I search on Madison, WI. This will show posts that were posted to the MADISON, WI CL site. It could be something located in Alabama, but generally, people list items in areas the item is located.
You can see Madison in the top circled in red along with "FOR SALE" as the category and I use "ALL for the sub category because grills can be posted in OUTDOORS or HOUSEHOLD or other sub categories.
Also, notice in this search I used "Weber Grill" as the search term. Sometimes it is better to use "Weber" only because if someone just lists the "Weber" for sale and doesn't use the term "grill" it won't tag it.
You can try different combinations of terms. I also search "Webber" occasionally as some people never learned to spell. I also search for just "Grill" sometimes as some people don't know the difference between a Weber and microwave oven. They just call it a "Grill". But, you will likely get a lot of useless results of other makes of grills, Car grills and many other items no where close to something you would want to cook a ribeye on.
Like I said before, the list in the top portion will only be items that were advertised in the CL for the city you searched on. Then, below that, CL will list items matching your search in nearby CL cities.
Now, this CL search is based strictly on your location and all items listed to any CL listing where the item is located within a search radius that you chose from a given zip code. So, you would put in your zip code and a search radius. Then input a search term such as "Weber Grill" and hit enter. It will display items that people listed showing a location that is within your search radius regardless of the CL city they listed the item too.
Again, I leave the sub categories all checked so I don't miss a Weber grill that is listed under Farm and garden or something even more silly.
FB Marketplace is a bit more entailed and confusing. I am thinking someone else can do a better job explaining that system.