You said " ATTENTION PEOPLE Gold sellers now have the ability to magically make gold" which is what I responded to. I'm not specifically speaking any single person, I'm talking in general like you were in your earlier post.
That said, I don't know if there are still ways to dupe or not because I don't follow the game nearly as close as I used to. Maybe there is or maybe there isn't.
How many accounts would it take to dupe 1P in gold?
I'm not really sure the exact steps that were used back in the day to dupe things, but I'd assume all you need is one account; even if you needed 2 chars you could just ask a trusted friend to help. A backpack can hold 125 items so if the person was duping a bag of checks (assuming 124 checks); they would only need to dupe that bag 8x. Again, I don't know how the duping was done (ie how long it took) but even if it was something to do with server down (ie once day) that's only about a week of doing it with 1 account to net the person 1P.
Now doing it with multiple accounts or being able to do this multiple times a day would exponentially increase that amount of gold.