I mentioned before that as an engineer, I'm not fond of marketing.
Image credit: Dilbert.com (Disclaimer: Liking the Dilbert comics is not an endorsement of Scott Adams' politics)
It's not that I can't be good at salesmanship either. I have a good grasp of communication skills and think I have a decent chance of writing good copy. My main issue is that I've been exposed many times to sales/marketing practices that just seem dishonest downright or scummy. This happens both with me as a customer and with me on the side of the company trying to do the sales/marketing.
An example in the software engineering sphere would be a developer writing project proposals in response to tenders, and he is asked to write a technical response confirming that their product supports a particular tender requirement. Except he knows for a fact that he doesn't, and when he raises this concern, he's told not to worry about and that they'll just implement the feature if/when they win the contract. And apparently that's a regular practice in some companies. Disclaimer: I'm not saying I have been personally involved in such a situation, but I do know such situations exist.
I understand the motivation from the sales side, but not only is that intellectually dishonest (to say the least), it also puts your engineering teams in a bind should the project push through - you now committed them to do an extra feature without proper estimation or scheduling and so on.
For me it's okay to sell something by promoting its strengths and advantages, but not by being dishonest about its capabilities or weaknesses. I suspect that this cripples me a bit in the real world where people with less scruples are more willing to bend the truth to make money. But for me personally, honesty and integrity are more important than making more sales.