Depends if some one knows what they're looking for, tells for me on the 3789 are: Chrono hand middle tail fin too long Gen has raised rings around the chrono sub dials Case side logo totally the wrong colour -- this one looks spot on ... I've just removed the paint completely on mine Mine has a gen tube and crown but to be honest from pics I couldn't tell if it was rep. So what is a tell then? It's fairly easy to google image iwc top gun and get pics of gens and reps, the rep pictures even are tagged with rep website addresses. How accurate do u want your rep? I know I'd like mine as near to gen as possible (I think I enjoy the process of sourcing parts and building it - rather than walking into an AD and buying one) so will be going to great expense to change as many parts to gen as possible ( proper Franken )