A listed flashing allows the inspector to see both top and bottom that there is clearance to combustibles. Also as noted, some factory built vents and chimneys require a gap or slots at the top of the flashing cone to allow for cooling.

That smooth pipe does not have the bead rolls of B-vent. Also, by info. provided, the B-vent is short. There should be a listed termination. If a vent is over 5 ft through the roof, it should be supported such as with struts or guy wires.

IF you don't see listing stickers on each section and component, call it out as suspicious. The rest of the B-vent should be visible in the attic or Combustion Appliance Zone but not always accesible.

HTH,
Bob

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