My personal fave is the T206 Wagner with Ty Cobb back
I used to know a renowned hobbyist back in the day who would patiently listen to folks’ stories about how they came into a collection and then briefly flipped through the cards - usually (but not always) reaching a conclusion that they were no good. Many of the things he looked at were obscure issues and I asked him point blank how he could be such an expert on so many varied cards - before the days of the internet were mainstream.
His answer was so simple it was brilliant. He knew the major issues well enough to know what to look for - but not the obscure ones. So he went by a few simple rules. If the cards he knew well were fake 1 he assumed the others were too. If he didn’t really have a handle on any of the obscure issues - at least he knew what the stars and rarities were. If a random collection was packed with those and few to no commons - he assumed it was fake … and he was almost always correct.