Alright, so the money making method is now basically dead so I thought I'd share my story with you guys. So flashback to a couple of months ago, I needed to supply my Ironman with votebooks. Using Guthans and AFKing Cave Horrors was/and still is aids due to everyone doing it and it is overcrowded. I decided to buy a Rune Crossbow and grind Zulrah instead, so I decided to buy a Rune Crossbow the only logical way I knew, which was using the TP. The cheapest Rune Crossbow was for 1m, so I went ahead and bought it and continued on my day. I later found out that Rune Crossbows were sold in the range shop for 16k... So I made an ALT account which I only sold Rune Crossbows on for a very long time, I would log in once a day to restock my Rune Crossbows and collect those that sold overnight. I made around ~15-20m a day doing this. Nowadays it has slowed down by a ton but you can still manage to pull 3-4m a day.
Here is a picture of me selling 19 Rune Crossbows for 250k Each within around 1-2 days.
Thought I'd share this interesting story with you guys, and sorry to anyone who bought my overpriced Rune Crossbows.
EDIT: And I've completely stopped doing this as of today.