I would support a grading system for fakes. Grade A might fool real professionals. Grade B might fool some dealers an collectors like me. Grade C might fool a beginner. Grade D might fool a person who has no experience with ancient coins. Grade F could be pulled out of a bag in total darkness and be identified as fake by feel alone. D would be liberal here.
Cast, plus the first pic's portrait appears tooled/smoothed around the edges to clarify the profile. So I think it's a tooled fake and something to steer clear of.
I strongly suggest you examine those images and read the descriptions to learn how to identify modern forgeries of ancient coins. http://www.forumancientcoins.com/fakes/index.php?cat=5
If your first instinct when getting into a new hobby is... "I'm going to go to eBay and buy something I know absolutely nothing about."....you've already set yourself up for failure and a world of disappointment. eBay is best left to intermediate/expert hobbyists, and even they accidentally get the occasional fake when shopping eBay. There's just that many fakes out there. In my opinion, ancient coins on eBay are 35% fake, 40% authentic but grossly overpriced, 20% authentic and properly priced, and 5% authentic bargains. That's not a minefield a newbie should be trying to navigate, as 3/4 of the time you'll end up regretting it.
Actually, it's okay to start collecting ancients via eBay provided that you start small and go slowly. I recommend that you keep all your initial purchases to less than $15. You will end up with mostly late Roman bronzes (LRBs), which I suppose is as good a place to start as any, and you are less likely to buy fakes in that price range. After a while you will develop relationships with some dealers that you can trust. Then you can start expanding your range. Also, look for auctions of coins you are interested in and bid $5.00 on them. (Be sure to consider shipping cost when calculating your bid.) You most likely won't win the auction (unless the coin is fake, and then you're out $5 for the lesson), but you'll learn what the coins finally sell for, and over time you'll develop a sense of the relative value of different coins in different conditions.
When on school playgrounds, Kindergarten students do not play ball with 5th graders. The ones that try, can get hurt. Starting a collection with Didius Julianus is a lot like going out for the high school team. It helps a lot if you have learned the basics when younger and put of a few pounds (knowledge and experience). You are welcome on the playground but we hope you will play safe. That does not mean you must start with late Roman but it does mean you need to avoid bullies and not get ahead of your peer group until you are ready. There was a time when we shook our heads at new collectors who started with coins of the 12 Caesars (first century AD) but now we see a few who don't want all 12 but just the rare ones (Caligula, Otho etc.) and act uninterested in the easy Flavians etc. The chances of buying a fake for your first coin is higher if your first coin is several hundred dollars. There are cheap fakes so you still need care but it is almost certain that a cheap coin of a popular/rare/short reign ruler will be fake. I like Sallent's numbers but believe 40% is low for grossly overpriced. I don't see quite 35% fakes unless you are only looking at the rare and popular coins. You can cut the risk down by buying from a seller you know. There are dealers who post here on Coin Talk. That would be a good place to start but the coins they sell might not be as rare and popular as your Didius ---- they would, however, be real.
There are certain issues of coins you should stay away from until you've researched them thoroughly. The coins of Didius Julianus and his family are one of them. By researched thoroughly, I don't mean looking it up in Sear or RIC to assign a catalog number to it, but being able to identify with which particular die pairs it was struck and seeing numerous previous auction sales to get an idea of the provenance of your prospective acquisition and an idea of the coin's market value. Moreover -- because a die match to a genuine example won't protect you from a cast fake or strikes from a cast die -- always buy such coins from well-established and trustworthy firms. Accusations of "don't play on my playground" notwithstanding, unless you can say (about a coin up at auction at Berk, CNG, etc.) "that sestertius was struck with Woodward obverse die 2, reverse die D, and a similar well-centered gF example sold at Naumann in 2017 for a hammer price of 875 Euros, and a VF went for $1200 at CNG in 2018" you shouldn't be buying sestertii of Didius Julianus. That's just my opinion. You are, of course, welcome to LEARN THE HARD WAY.
All of the above advice sounds pretty intimidating. But it's good advice. Just don't let it scare you off. This is a great hobby. Welcome aboard, and feel free to ask questions of us on this forum. Most of us love to help.
