The wear and nicks on the rim compared to the rest of the coin. I'm no expert, and I'm not calling it counterfeit, because the difference in wear could be explained by cleaning.
Rim took a lot of abuse in bags. High spots wear quickly on these. Fields and especially around stars quite protected and wear slower. Low grade trade dollars quite rare. You seldom see one below vf. With the exception of pocket pieces and a few of the western mints that ended up with a fair amount of use. Lowest grade i ever had was a g-4 1874 that had the pocket piece feel. They didn’t circulate a lot especially after being demonetized
I just looked at two 78-S pieces on the PCGS site. Their denticles had much narrow spacing on the reverse. I did'nt look at your obv pix: too low res. I'd say counterfeit but then again I'm not an expert on these. The porosity really is not nice and leads to questions on authenticity.