It's not at all a no-go area. The Tenderloin is one of the most expensive and desirable neighborhoods in SF. It's no worse than the Mission or 6th and Market. It's definitely the best place I lived in all of SF, including the Mission, SOMA, and the Sunset. No wonder people are paying $3-4k a month for studios there. Yes, there are drug spots and such but it's definitely not a place to fear or avoid. That's nonsense.
This is the first time I've heard about The Tenderloin being a desirable neighborhood. Are you sure you were actually living in the Tenderloin and not one of its adjacent neighborhoods?