The Phrogues came to Zaonia. Zaonians knew there was intelligent and nonhuman life out there. Most of them leanred all they knew about aliens from the movie serial Ghouls of the Underworld. Despite this the Phrogue ship opened friendly relations by radio after it entered orbit.
Trade began as the Zaonians had some useful metals the Phrogues wanted for fabrication and couldn't be bother to dig up or crack asteroids for. they baubles and gadgets they traded were immediately seized by the Tech Knight orders.
A number of officials in the civilian government and the Order of the Flaming Sword were concerned about the Phrogue practice of buying or renting warehouse space. Nothing went in or out of the warehouses except Phrogues. To be fair the Zaonians would be suspicious of humans doing likewise.
Then the Profit Rockit broke out of hyperspace and grounded. It turned out the Rockit had met the Phrogues and exchanged pleasantries via radio and in person on the ground. In fact several Phrogues insisted on coming onboard the beat up freighter to socialize.
The Tech Knights, police and the Mayor were waiting to have a gentle word with the crew about the Phrogues. The Phrogues, however, had made the freighter crew sign a non-disclosure agreement so draconian as to make threats of death rays and giant robots seem passe.
Sir Cuthbert argued that shooting one of the crew might loosen some tongues. But it was a ship mortgaged and operating from Zaonia and they had no real criminal record. The captain of the Profit Rockit, however offered a solution. Second tier Navigator Sandoval came up with the solution but Captain left that part out. He, Captain, would go to the Phrogues and explain that their NDA and actions were causing concern that would impair future business dealings. That an explanation should be made to the leaders at least, who could sign similar agreements and come up with some bullshit story that wouldn't hurt the Phrogue profit margin and would avoid torch wielding mobs.
Vokh, the lead Phrogue thought it over. The concept of bullshit stories had to be explained in fair detail. Navigator Sandoval, having met a few aliens, was tasked with this. She was also an expert on bullshit. After a long discussion Vokh agreed that she should tell the senior Knight and Mayor. They happened to be the best bullshit artists around in her estimate. The Phrogues gave her a retainer to develop an algorithm to determine mastery of bullshit for them. That's another story.
The Profit Rockit met the Phrogue freighter as the humans were outbound. The Phrogues werea inbound but obliging enough to eat the extra propellant and rendezvous, eager to test the human markets out here on the Rim.
The meeting was a fiasco. The Phrogues had all manner of things the humans could trade and make locals pay dearly for: holographic textiles, stealth prosthetics, cybernetic teeth (which the humans didn't even realize they needed). The problem was the humans had nothing the Phrogues really needed or enough credits to afford goodies.
Then the crew had an embarrassing moment. A tet crab showed its ugly face analog. the crew already had a couple of incidents, leading to nipped toes and a ship's cat that was strongly considering quitting. The crew even exposed the ship to vacuum. Apparently that wasn't sufficient. the creatures had lodged in the deepest recesses and they retained enough atmosphere to at least let eggs survive.
The crew had begun carrying sidearms. Even Sandoval had one though it made her list to one side. there was a pause in the story here as the Mayor and Sir Cuthbert exchanged sympathies with Captain. Tet crabs were all over Zaonia and the reason the Zao didn't suffer from rats. The crabs ate them. Sadly their hunger extended to canines, felines and just about anything else organic. Zaos hated the damned things. they didn't load their shotguns with birdshot, they loaded them with crab shot.
Captain Vokh, however took it in stride, gave a loud sniff and then attacked with a barbed tongue nearly as long as Sandoval was tall. The tet crab vanished formidable claws and all into the Phrogue's mouth and Vokh asked how much he owed them then remembered his manners and apologized if he'd eaten anyone's lunch by mistake.
The Profit Rockit remained docked to the Phrogue freighter for two days until the aliens did their best to clear every crab from the ship and paid handsomely for the privilege. They were nearly out of fresh food themselves. Vokh even took pity on a very upset cat with kabourophobia and outfitted her with an individually made suit of feline battle armor. That's another story.
So the reason the Phrogues were renting or buying warehouses was far from sinister. Warehouses bred vermin. the Phrogues wanted to keep the price of tet crabs from spiking (current price was 0 cr. per kilo). The Phrogues to their credit knew they weren't going to keep their secret forever.
One specie's vermin was another's entree. Or at least fast food.