I've finally gotten around to getting my 20 Days of Gold Making on the go! Thanks to @NevAHAddict for providing the idea to us all :)
My biggest OOPS? Honestly in relation to gold making I can't say I have one. See for me I'm a very reserved player of the AH. I don't really make mistakes on it, I'm patient and just slowly build in the guild via the AH, other than that, most of my gold comes from farming, boosting or using peoples brains against them. Does that mean I'm perfect? Far Far Far from it.
Lets take a simple mistake I've made in the past, which I think we've all done at some point. Pricing things wrong - one of my biggest issues when I started was pricing things by stack price, not individual item price. So as much as I thought I was making "profit" I could of been making a hell of a lot more. Personally I see that as a small thing, however you can learn a lot for these smaller mistakes - so instead of looking for the one big mistake - take a look at all the little ones, since sooner or later they'll all add up to one huge OOPS!
Thanks for reading.