yeah i had a huuuuuge success rate last night after watching that japanese video (thanks whoever posted that). however i use the del perro heights apartment. im convinced that you can do this glitch at any apartment. you just need a few things: 1. 2 apartments in the same building 2. a car you want to dupe in garage A and a space for the dupe to go in garage B 3. ideally, an already existing situation in the built environment that allows you to park, have your doors blocked so that you warp in and out of your car. (for me, at del perro, this is inbetween the two dumpsters on the other side of the parking lot adjacent to the garage, roughly 200 feet away) (note: i have personally found this method to be WAY more reliable than the previous methods, ie parking the duper/original panto out of range of the garage door, this will be further explained)
now, you follow these steps to create the dupe, and continue duping. (i do this in an invite only, solo, but i guess you can do it with friends, no testimony on the buddy version)
THAT WAS HOW TO DUPLICATE THE VEHICLE. TO SELL THEM FASTER THAN 1 EVERY 48 MINUTES (IRL), YOU MUST DO THE INSURANCE GLITCH TO BYPASS THE WAIT.
noteworthy mentions: - i have spawned directly into my garage after quitting the mission. it seems there is a way to tell right before it happens. if you see the black mission screen FADE out as you quit, it will spawn you in your garage. if you see a harsh transition (no fade whatsoever) after quitting the black mission screen, you did it correctly and will spawn outside your garage. i can only offer the same speculation that you all have on this: maybe you quit too fast. it seems to me, that you can not quit too slow, but it may reduce the time you have to realize you are outside and then to warp into the original. - if you see a 'bricked' (un-enterable) NPC car blocking part of your garage door, you can still get this glitch to work (i had a brick there for 3-4 of my dupes last night). you do nothing differently. however it seems that the above mentioned fade out has more potential to happen. but, i had not had it happen 2x in a row, even if the brick is still there. if you want to ensure the brick is not there, just drive around the block. it should despawn.
sorry for the super long post, but hopefully this will eliminate questions and pointless, "i cant do it, dont try, doesnt work" posts. If you have a question for me, i will try to answer it and add it to this post ASAP.