Sestertius AE, Rome. Very heavy and slick, is there a reason for that? Anything to worry about on this coin. Savoca Auction
What's the weight? Generally, Savoca is very reputable. I've purchased many coins from them and they're one of my favorite auction houses.
I'm not an expert in sestertii, but the diameter is well within range. The weight is a bit low, but not unheard of for the type. The seller is reputable. I have no references on these coins, but from a search I think it's RIC IV 541. It seems genuine to me, but keep in mind that I don't own a single sestertius myself, so I'm not the best resource.