In 2370, he and his ship were detained at Deep Space 9 for seversl hours while station personnel investigated allegations that the Kressari were being used as an intermediaries by the Cardassians to supply arms to the Alliance for Global Unity. Zef'No protested his detainment and even threatened to get the Kressarian government involved. He was eventually allowed to leave after Odo had been stowed aboard.
Following the Calondon's departure from DS9, Zef'No rendezvoused with a Cardassian gul, who transferred several weapons aboard, after which, Zef'no had the transaction confirmed by the Cardassian's thumbprint on a PADD. The entire transaction was observed by Odo, while in tbe form of a rat, who surreptitiously "borrowed" the PADD as evidence. (DS9: "The Circle")