I follow two auctions, one denarius of Antoninus Pius and antoninian of Philippus with starting price of 50 eur. Are these coins genuine and which is the fair price? Thanks in advance.
They are almost certainly genuine. When bidding, keep in mind the buyer's charge (often about 15%) and the cost of shipping. Depending on where you live, a 60 Euro winning bid will turn into a 100 dollar coin.
Without considering anything other than the coins themselves, I think the Philip is the better of the two. However, they are both of equal value IMHO.