What's the fastest way to make Echoes (money) in Echo Bazaar?

What's the fastest way (fewest actions) to earn the most valuable commodities?

The fastest way I've found so far is in Mahogany Hall; it requires a very high Persuasive skill. If you train the Louche Devil and teach him Philosophy, you'll get 111 Nevercold Brass Slivers per action and increase your Pygmalion quality. When Pygmalion reaches 17 or 18, you should be safe to take him out to a Society dinner, which gives you 1000 bonus slivers. ... You can then re-train him as often as you like to rack up lots of Echoes.

If you want to do it with your Dangerous, head to the third coil of the Labyrinth of Tigers. "Avoid becoming an exhibit yourself" and "Fight back" for ~1 Echo per action. (Most of the actions in the third coil earn ~1 Echo per action, but they require a very high Persuasive as well.)

This is a difficult one to answer; given the link between Stories and Qualities, it will be different dependant on what is available to you.

As a general rule, completing a series of linked Stories will carry greater reward, but this can become inefficient if the Story is difficult for the determining Quality (failed attempts receive no monetary reward).

As for a specific tip; I would recommend searching the ruins in the forgotten quarter in the early game. The reward for the lowest level option is based solely on luck, and the cost of entry can be reasonably quickly reclaimed. 10 x relics @ 5p with a 50% success rate = 25p/adv.