One of the more devious ones I see in the tech world is not a direct lie per se, but more of a "assumed misconception." For instance, imagine have 2 regular US Mint-issued quarters. The only difference between the two is one was minted in 1992, and the other in 2003. Both are worth exactly 25 cents. Now suppose I want to sell you the 2003 quarter. An "assumed misconception" would go like this:
The 2003 model of the quarter has been taken as the accepted standard where cash is accepted anywhere. Steps have been taken to assure the consumer that your 25 cents is not only accepted by all modern vending machines, but is backwards-compatible with older machines, and is now assured tender for ALL cash transactions.
Well, so is the 1992 quarter. But someone who didn't know they were the same might assume that the 2003 has been "updated and modernized," and thus, worth more. Now here's one a politician might use:
The 2003 quarter was minted after 9/11; minted when the US had much stronger security in place. The 2003 quarter has anti-counterfeiting measures put in place by a new ISO-9000 standard.
The security of the US Mint has nothing to do with the value of the quarter at all. Anti-counterfeiting has been in place ever since any money was ever minted anywhere. The ISO standards are meaningless to the consumer in this model because the end value is still only 25 cents.
I bring this up because today I took it upon myself to learn about an application known as Cold Fusion (some of our customers use it, I wanted to know more about what it does and how it works in case I run into customer problems about it). It's a website designer, to put it simply. But to listen to the demo, and read the specs, you'd think they'd solved dozens of problems plaguing the Internet, and a lot of them are flagrantly "flouting" the Gricean laws of Quantity (Do not make your contribution more informative than is required), Relation, and Manner (Avoid ambiguity). One they bring up is how you can now print your web pages. Wow-wie! Or use tables that can be imported and exported into documents. ARG... so can most of their competitors!
Sorry... had to rant.