I would submit that even good sales people use FUD in their pitches - they just don't do it overtly like the weak sales person mentioned by the OP.
Implied FUD (i-FUD) if you will...
example:
If company A has a flaw or defect of some kind - or simply lacks features and/or integrations in their products - the sales person for company B doesn't have to mention company A at all.
Instead, if they focus on Feature 1 and Feature 2 that their own Company B products have - and why they are so very important to have - there is then no need to point out that you should be 'afraid' of using company A's products because they do not have them.
Example:
If I were a sales person for Cam Co Z and I know that the customer is deciding between my cameras and Arecont cameras - I would spend some time in my pitch talking about all the time and money my customers save by having a reset button on the outside of the camera.
If I am persuasive in telling the story of the need for a reset button (by conflating it with real value) then I've employed i-FUD... the customer believes a reset button is of real value.
Hopefully, I get to pitch the customer before the Arecont person does... ;)
Disclaimer: I only use Arecont (and their lack of a reset button) as an illustrative example in my comment above. I am not making any comment about the strength or weakness of their products, and none should be inferred. :)