Buy what you could actually afford and nobody will ever ask. Also, if you have a reputation of being highly knowledgeable about watches and always volunteer to help others in their purchases, nobody would dare call you out. Also, considering the time I've spent on this forum and how rare and awkward this hypothetical situation would be, even I would be uncomfortable judging a replica... but because of my career, lifestyle, and confidence, and the fact that so many people know I have bought and sold and collected watches for a decade, I have no problem wearing a 6538 as a gen...
If someone REALLY got down and dirty, I would say, "Look man... since you know Rolex, you know that this watch would cost anywhere from $25K - $75K in this condition, but check this out... this thing was built for me by a guy in Nicaragua from service and replacement parts that he sourced over 6 months... it actually has a modern movement in it, too... it is SO much cheaper to go this route, and I am so impressed by the idea that I am going to start sourcing the parts and building them myself..."
If someone told me that, I would be SERIOUSLY impressed and probably be like, "So wait, how can I get a watch like that built for me?"
The modern watches, nobody would ever ask, but if they pressed me I would probably say, "Look man, I got sick of blowing so much cash on watches and I found out that there are crazy people out there that build these dead-on replicas... SOOOO much cheaper and you can even get them with the same damn movement. It will still cost you around, I dunno $500 or so..."
It's true... I remember when I finally learned how pointless it was to buy a gen when I bought a U-boat Flightdeck 55mm... the movement was a straight-up 7750.... with a rep quality engraving... MIGHT AS WELL BE A REP, SAME DAMN MOVEMENT!!!! So I have no problem with the "is it real" question because these days, the line is so blurred on quality and movements and the used market is so saturated with replicas and service parts that I guarantee there are tons of people that are wearing a Rolex with a gen movement and case and that's it and paid full used price for it, or wearing one of the countless 7750 variant gens that is actually (unbeknownst to them) a replica and they are happy as a lark.
And I will tell you another thing, the amount of belief that people have in your watch (in my experience) is inversely proportional to "how hard you try." I often go to Publix dressed almost like The Dude and look like a complete mess, but wear a PAM or my 6538... but I act incredibly astute and polite to everyone. I have also been stopped in the parking lot looking like a mess with a "Nice watch, what is it?" and say "It is a 1959 Rolex Submariner..." and have been given the "C'mon, really?" stare, and respond, "Well actually the case is from a 5508 but the rest of it is from a 6538... if this thing were all original it would be $70K! It was pieced together from parts..."
The key, I think, to any kind of material possession is the mindset of "this is for me, not for you," and that is how it should be because 99% people don't know/don't care.
And even when I was a wage-slave, I had a gen Breitling and two gen Tag Heuers, so it is completely legit to have a nice watch if you saved up and got one... I know a lot of kids who received them as high school or college graduation gifts.
Sorry about the rant.