Introduction: Linked items is a term I used to describe items that have their prices linked in some fundamental way. In that sense, the rise/fall in price of one item will eventually result in changes in price of the linked item(s). By carefully watching the prices of two linked items, you can make rapid, short term merches (<1 week) to make lots of gp.
Basic example 1: The items air orb, battlestaff, and air battlestaff are forever inversely linked in price. The air battlestaff price is fixed by the alch value of 9300 gp. If the price of air orbs goes up, the price of battlestaff will deter people training crafting using this method. Thus, the supply of battlestaff will outweigh the demand , and price will drop to the equilibrium point. Vice versa, is the same.
Basic example 2: The items zulrah scales and antivenom are directly linked in price. If the price of zulrah scales increases, the price of antivenom should increase, as zulrah scales are used to make antivenoms.
Advanced example 1: The items of the air battlestaff are also (in an abstract, long term way) linked to the cost of training crafting. If for whatever reason, jagex gives everyone free 200m crafting exp, the price of both air orbs and battlestaff will drop. This is because players will have no reason to make air battlestaves unless it's for profit, and for there to be profit, the prices of orbs and battlestaff combined must be less than 9300. For a more realistic scenario, see how the introduction of wyrm/drake bones crashed the price of dragon bones.
Advanced example 2: The items of zulrah scale/zulrah uniques are directly linked to the price of high end magic gear (mages book, eternal boots, etc).
Those are the two graphs of zulrah scale and eternal boots, just to show you I'm not spewing shit out of my ass.
Why? The profit of zulrah increases as the price of scales goes up (doing zulrah is net positive in scales) and some other reasons out of this topic's scope. Magic items make up the more expensive gearing options for zulrah.
Advanced example 5 (I actually did this): Yesterday the price of antivenom spiked up to 8k from 4k, likely due to zulrah-related updates causing market instability. This graph shows a small blip where the price spiked (graph not 100% accurate on real trading price).https://gyazo.com/d1aa8328a6dd73056ad84550ea3590e9
From this, I hypothesized that antivenoms, in general, were going to spike in price. I noticed that antivenom+, was still trading at its normal price even though its weaker version was spiking at 8k. This graph shows how the antivenom+ spike was ~12 hours delayed after the spike of antivenom. https://gyazo.com/1990e761cec0b0382686ff48ac7516e4
I bought ~10k antivenom+ yesterday, using as many accounts as I could, and made ~1k profit on each of them, for a total of 10m in 15 minutes of runescaping.
Thank you for reading, I hope to provide more insight in future posts on how to successfully make money off the grand exchange.