I can't think of any huge mistakes...

I mean, I had a Manager try to coach me on sales when I first started. I did exactly what they told me to do, my numbers died. I then promptly ignored everything they told me, and my sales skyrocketed. The mistake was telling them that I ignored what they told me when they went to congratulate me/pat themselves on the back for their coaching.

This happened during one of our early Sunday morning meetings:

Manager: See? This is what happens when follow my lead! Isn't that right Rasimov?

Me (Barely awake since it was 7am in the morning): Huh? Oh, I tried what you told me to do, but my numbers died, so I did my own thing.

Egos were hurt. However, my numbers kept going up, so they couldn't really do anything, but they threatened to write me up for undermining their authority or something. I then said I would report them to HR.

Before I fucked up too much with them, they got demoted and a new Manager was hired.

They seem to be the same, basically, completely clueless about sales, but wants people to "sell" how they they tell you to sell, and they have no fucking clue how to sell.