Hello and welcome! I will almost bet that the performer would be like brand new being a 2016 model even if it sat out without a cover. Plus, you are saying no rust and looks clean from the pics. It should be fine. On the older Performers, I would check for a damages on the table, lid, and a bowl, and gas assist starting sys. but with this one..... if the price is right, just do it! Pick it up.
My first gen3 performer sat outside for 5 years with no cover. When I went to pick it up, it was full of wet charcoal from lid vent open and the ash pan was full of water. I got it at a good price so I picked it up. Once cleaned up, it was like new condition. Gas assist was never used but worked fine when I tried it. No rust inside the bowl.