In my story, there is a character who can go back in time, and has done so already, for the purpose of getting rich. He is not the main antagonist, neither is he the main character. He is mostly just a guy who saw a chance to get a ton of money and took it, and will obviously be important to the plot.
His "get rich" technique went like this. Bring with you, either in paper or virtual format, many interesting stories, books, movie scripts, etc. I haven't decided yet exactly how far he went in the past, but let's assume he has no trouble reading his stuff, so no more than a few decades.
Then, back in time, he "writes" himself big hits like Harry Potter, to get all the money and fame instead of J.K Rowling. He does that for several big media. He copies them word for word, and releases them early enough so that the "real" author can't go to court with their own manuscript, because they have no such thing, and even if they do, everyone thinks they copied our guy's book, and not the other way around.
It works pretty well, and he earns a reputation for mastering several different writing styles and settings.
My main character is aware of the existence of time travel, but has not used it himself yet. He lives in the "past" that our con man travelled to. Time travel is not widely known, and both those guys encountered the information by complete chance.
I'm looking for a way to figure out the con's scheme from the past, when all you have is a vague suspicion someone is up to something through time travel, because they need specified tech for another purpose.
The setting is not final, but it goes like this: in 2010, mr X steals time travel technology from evil corp, and uses it to get rich in 1990. Evil corp has no way to reproduce the technology, but has already sent one more guy a bit earlier for their evil plan. Main character in 1995 is aware of evil plan, and tries to stop it, and his only chance is by borrowing/stealing time travel device from mr. X in 1995 and use it. Main character would not be thrilled by mr. X's scheme, but also has more important priorities so wouldn't mind allying himself with him if required. Mr X didn't plan on using the machine again, but is doing all in his power to hide its existence while still making millions.
I am looking for a way to see through the scheme enough to at least make contact with mr. X, even without understanding the whole thing. What mistakes are either unavoidable or very likely to be overlooked when using that plan? What signs are noticeable to someone who is aware the tech exists, but not where it is or if even anyone has used it?