I suppose you could get weeded out for "soft factors" like attitude or oversleeping every morning, but FO's on IOE usually have zero pax interaction.

Usually people (new to 121) fail IOE for visual approaches or descent planning. A check airman buddy of my mine at mesa told me about a young lady who had to be prompted to descend every time (after being given PD)...he told her on the last day that she was going to have to plan and execute the descents and that he was going to say nothing. Well, they arrive over the destination airport (BFL ?) at F290

On the visuals, all the automation tends to get people...it works great when vectored 10 miles outside the marker on a real approach, but on a short dumped-on-the-marker visual you need to turn the AP off, get slow, get dirty, then descend and turn as needed. People new to jets tend to be afraid to arrest their descent to slow down so they can configure...if you don't get configure first, you simply can't go down and slow down.