After putting a stop to fraud the Tech Knights of Zaonia (0104 C885655-5 Ag Ri 123) saw more opportunity for economic growth. In an interstellar polity that had all manner of cyber crime their security was an order better than most simply because it did not rely on computers. The First Bank of Zaonia worked on a system of handwriting. People who were recognized customers had their signatures filed and simply signed for things. That was the first level of security. The second level of security involved established handshakes, photos, mannerisms and yes passwords ... that were spoken to confirm identity.
No hacker could break the system. Any impersonations would require a master forger, who was also expertly disguised, and managed to learn memorized passwords and recognition cues from the customer. That was a tall order for most.
The subsector nobility noticed and began making deposits in the banks in the form of precious materials. Lock boxes were used to hold various secrets: letters for blackmail, contracts for unholy business alliances, family heirlooms, and artifacts.
Zaonia now had a foolproof defense against offworld invasion. Any would be conquerors would have to deal with their depositors, who were not, the sort to let their valuables fall to others.
Raids were the problem. The security forces had rifles and submachine guns. Manpower was there. they could get a lot of men with rifles or submachine guns and mass them at bank vaults. That wasn't good enough. raiders with battle dress would probably have surprise and high energy weapons.
Worse, high energy cutters could let them into the best vault the locals produced in a few minutes. Offworld experts agreed. The biggest most massive bank the Zaonians could produce would fall to a determined force of offworld pirates.
The locals could hire mercenaries with high tech weapons to guard their bank but that involved offworld technology which the local technocrats did not produce. This would undermine their expertise and authority and what would keep the mercenaries from looting the bank themselves or looking the other way when bribed?
So the locals built not one bank but many many banks. Small ones. They were still guarded pretty well. they all had smaller but hardened steel vaults. Most of them were empty.
Armored cars shuttled between the banks on a daily basis. Most of them were empty but the few held valuables that were constantly shuttled between vaults on time tables known to only a few. Each of the schedule writers only scheduled a specific route, one of many. If anyone did hit the right bank or armored car that schedule writer would have hard questions asked. The schedule writers included watermarks specific to each armored vehicle crew. Any photocopies could be tracked to the person who lost or sold them.
Raiders could hit a bank. They would be shot at by a number of guards. The hail of bullets would be too risky unless the raiders had battledress and still be risky even then. After fighting these defenders the raiders would open the vault, which could be empty. Ditto for the armored cars.
Eventually the locals dug an underground roadway system (remember the cheap labor?) They dug stations under each bank to allow the cargo transfers to occur out of sight. By now the banking business was really taking off. It became a major planetary industry between, security, excavation, construction, maintenance, tank manufacture, and administration. A few people attempted raids but they got squashed quickly. Most of them hit the wrong bank or the wrong car or had a tunnel collapse on them. Oh yes: the tunnels were boobytrapped. They could make a suit of armor that could laugh at bullets, but no one made armor that stood up to a couple of tons of rock.
Fortunately low tech does not equal stupid. After all, there are barbarians in space.