As you work through the episodes in Bangkok, in addition to having to choose sides between the Yakuza and the Triads, you can also earn faction points as you do jobs. This faction can be used to buy several good items and even some businesses:
When you do a job, you can get +3 faction for whatever side you help, and -1 faction for the opposing side:
You can total up to 1500 faction. Once you crest 1400/1500, you achieve "allied" status and can get all of the associated rewards:
Here's the thing - each time you do a job for one faction, you gain +3 and only lose -1 from the previous job. As a result, with some work, you can actually max out both factions.
The best way to go about this is to completely max out 1 faction first, like I did with Yakuza above. That way, when you do jobs for the Yakuza, you aren't actually losing any Triad faction (since it is already at 0). Once Yakuza is maxed out, you can then max out your Triad faction.
The end result of this is that you will have 1000 Yakuza Faction and 1500 Triad Faction. Now, max out your Yakuza faction again and you will end up with 1500 Yakuza and 1333 Triad Faction. Repeat this process a few times and both will be very close to 1500 points, and you will be able to buy whatever faction rewards your heart desires.
Hostile: 1-199/1500 faction
Suspicious: 200-399/1500 faction
Neutral: 400-699/1500 faction
Trusted: 700-999/1500 faction
Honored: 1000-1399/1500 faction
Allied: 1400-1500 faction
One catch, though. As you may have noticed (or heard), as you level up through the tiers, your costs for doing jobs goes up. Take a look:
Same episode, same faction, but the energy costs for jobs in Episode 1 on the 4th (Diamond) mastery are around double the cost of doing the job the first time through. So, what you should ideally do is at least max out one faction (taking it to 1500) by repeating a job like "Intercept an Ammo Shipment" repeatedly on the first level of mastery. Then, later, you can max out Triad faction in episode 2.
While energy costs increase, faction gained does not increase as you rise through the tiers.
Note that "Set Up A Phony Business" is an episode 2 job, but the first time through it still costs less energy than many of the episode 1 jobs at the second time of mastery or later. In other words, if you already missed the opportunity for cheap faction since you finished episode 1, you can always go to episode 2 and get your faction there.
In short, get your faction in early so that you can buy all the cool items and businesses for both sides!