Warhammer 40,000: Inquisitor - Martyr

Maybe this helps ?
Me and a friend of mine sold and buyback a red item over and over again and though the achievement tracker does not update right away, after backing out to the main screen and logging out and back in again (LB button on main screen) we added about 40% to the tracker for just 5 min work! We kept doing this until the achievement popped for us.

Greetings Inquisitors. To complete this achievement you need to acquire 5000 fate points. This is cumulative as pointed out above so you can use as many different characters as you like. I would recommend that you leave this achievement till last, as I did, as you will get a substantial amount through normal play.

There are several ways to acquire fate points:

1. Completing story arcs. There are usually a number of main missions you must complete to complete the ‘arc.’ Doing so will reward you with fate points alongside gear. You’ll know you’ve finished a story arc as when you return to the bridge after your last mission you get a message that pops up to that effect.
2. Completing any mission will reward you with 1 measley fate point. However, you can increase this number (and indeed other mission rewards) by using an appropriate tarot card. There are plenty available, I used the ones that increased overall rewards by 50%.
3. Priority assignments (available from Remigus Klemet on the right side of the bridge)
4. Selling rare gear (red items) can yield some small amount of fate too.

However, the most effective ways for gaining fate I list below:

1. Weekly glory. If you accrue 400 weekly glory then you will be rewarded with 150 fate points. Glory is accrued by completing any mission. Check your progress on the glory option on the menu wheel when on the bridge.
2. Weekly challenges. These yield something like 25 fate points per challenge. View these by pulling RT when on the bridge.

(My two favourite methods)

3. Void missions. These are accessible on a table to the left hand side of the bridge. You need to acquire ‘void shards’ to start a mission then you will have access to lots of missions within that. I found if I stacked a mission high with appropriate tarot cards then I could pop 10 fate points each time.
4. My absolute favourite method, though, was putting some time into the ‘system influence’ system. If you go to the star map, hit LT to view sectors and systems, then select a system and tap ‘y,’ you will see your current level of influence in that system. You receive rewards based on the level of influence in that system. The rewards range from getting tarot cards, to relic items, to that all important fate. You will need to pick a system that you know rewards fate (you can flick through the rewards before you earn them to see what there is). Some of them will reward fate on several occasions, the top reward being 300 fate points for accruing 800 system influence points. I was sat at 57% on this achievement and, through using system influence, managed to pop the achievement in a day or so. Remember, if you run out of missions to play in a system that you still need influence for, switch character and the missions will respawn!

I think that’s everything I can remember, I hope this guide is helpful. If anyone has anything to add please let me know and I can put it into the guide.

The Emperor Protects!

Just a note that this is a cumulative achievement. You do NOT need to have 5,000 Fate points all at the same time, and this carries across all playthroughs and all characters. You simply need to acquire 5,000 points in total.

One thing of note is that the game does NOT seem to count the lump sums of Fate points you get when you collect all the clues and complete each campaign mission. At least it didn't for me.