Looking to buy a used camera

First of all; sorry if this isn’t allowed here just rolling the dice.

I found a listing for a Pentax K1000 online with a 35mm and 50mm for a fair price. I’ve never purchased a film camera from a marketplace listing before so what should I ask or check to make the sure camera is in working condition? Seller is a photographer so I feel like this listing is a bit more reputable.