If you don't want to build a stash, don't shop sales! I started out doing well, but then the LQS had an "end of bolt" sale where if you bought what was left on the bolt, it was half price.
And then I'd be traveling, and visit shops and places like MSQC and Marshall's Dry Goods - and end up buying for stock just because the prices and select was so much better than I could get locally.
And then I went totally over the edge - one of the two fabric shops in my home town went out of business - at 75% off, I really went to town! I'll admit that I love my stash, even after just moving it to a new home. But that process made me motivated to use up as much as I can before I retire in 9 years and have to move it again!