How did Petyr Baelish increase tenfold the revenues at Gulltown?

Question

Reading the Game of Thrones wiki entry for Petyr Baelish I just learned that

Petyr ingratiated himself into Jon's services, first as a customs officer at Gulltown, where he increased the port's revenues tenfold. Seeing Littlefinger's financial acumen, Jon was easily convinced by Lysa to later bring Littlefinger to the royal court at King's Landing, and make him Master of Coin on King Robert Baratheon's Small Council.

Do any of the books explain how this character accomplishes this feat? For sure Petyr Baelish is intelligent and cutthroat, but do the books explain specifically how he increased the revenue of Gulltown, the Vale's greatest port? Did he just optimize a neglected workflow? Did he use force as much as brain ("persuading" influencing personalities, using extortion, blackmail, etc.)? Did he just use his intelligence and a good use of spies, incentives and bribes?

What did he do specifically when he was controller of the customs to increase the revenue by so much?

Answer 1

The answer will have to be from the books as the show has no info in this regard as far as I know.

First thing first, There are varying accounts about his earlier performance. Tyrion says Littlefinger increased Gulltown's revenues threefolds and that It was the Crown's revenues which were increased tenfold. Lysa Arryn says he increased Gulltown's revenues tenfolds.

Ten years ago, Jon Arryn had given him a minor sinecure in customs, where Lord Petyr had soon distinguished himself by bringing in three times as much as any of the king's other collectors. King Robert had been a prodigious spender. A man like Petyr Baelish, who had a gift for rubbing two golden dragons together to breed a third, was invaluable to his Hand. Littlefinger's rise had been arrow-swift. Within three years of his coming to court, he was master of coin and a member of the small council, and today the crown's revenues were ten times what they had been under his beleaguered predecessor . . . though the crown's debts had grown vast as well. A master juggler was Petyr Baelish.
_{ACOK - Tyrion VI}

And

My father said he was too lowborn, but I knew how high he’d rise. Jon gave him the customs for Gulltown to please me, but when he increased the incomes tenfold my lord husband saw how clever he was and gave him other appointments
_{ASOS - Sansa VI}

I would say he used the same tricks he used when he was master of the coin, if that performance is built and perfected from his previous way of making the dragons breed.

He did not believe in putting gold in a vault and locking it up. He used to invest the revenues in ventures to generate more revenue. Furthermore, he was great at picking the right men for the right job, which enhanced efficiency of bureaucracy and therefore the revenues. He did not care for a man's birth as long as he was fit to do the job. And almost always, these men proved to be more qualified than their highborn counterparts.

Oh, he was clever. He did not simply collect the gold and lock it in a treasure vault, no. He paid the king's debts in promises, and put the king's gold to work. He bought wagons, shops, ships, houses. He bought grain when it was plentiful and sold bread when it was scarce. He bought wool from the north and linen from the south and lace from Lys, stored it, moved it, dyed it, sold it. The golden dragons bred and multiplied, and Littlefinger lent them out and brought them home with hatchlings.

And in the process, he moved his own men into place. The Keepers of the Keys were his, all four. The King's Counter and the King's Scales were men he'd named. The officers in charge of all three mints. Harbormasters, tax farmers, customs sergeants, wool factors, toll collectors, pursers, wine factors; nine of every ten belonged to Littlefinger. They were men of middling birth, by and large; merchants' sons, lesser lordlings, sometimes even foreigners, but judging from their results, far more able than their highborn predecessors.
_{ACOK - Tyrion VI}

Answer 2

We Do Not Know

The books only have the following passage about how he did it and seeing as Petyr always acts in the background is sensible to assume his methods are not known.

Petyr's breath is always fresh . . . he was the first man I ever kissed, you know. My father said he was too lowborn, but I knew how high he'd rise. Jon gave him the customs for Gulltown to please me, but when he increased the incomes tenfold my lord husband saw how clever he was and gave him other appointments, even brought him to King's Landing to be master of coin.
_{A Storm of Swords, Sansa VI}

It's also worth noting the following passage about the Arryns from Gulltown who are noted to be rich from marrying merchants.

There are several branches of House Arryn scattered across the Vale, all as proud as they are penurious, save for the Gulltown Arryns, who had the rare good sense to marry merchants. They're rich, but less than couth, so no one talks about them.
_{A Feast for Crows, Alayne II}