After playing the AH manually for a long time, I'd know that a stack of ore would sell for 20g. I was manually buying when under 20g and relisting. My script just reduced the tedium. I'd manually add in checks for each high-volume item. It was super-hacky, but so effective, I didn't need to improve it.

One script would iterate over every item in my inventory. If it matched a hard-coded list, it would auto-list it at the hard-coded price. Another script would scan every item on the AH, and if matched another hard coded list, it would buy them.

Another story, pre-script. WOW had the inscription update incoming, which used flowers to make glyphs. I correctly assumed the demand for Peacebloom (tier 1 ingredient) would skyrocket once the patch hit. I spent three weeks buying everything on the AH, using multiple characters to store it all. The night before the update, I listed it all for 20x the normal price. The next morning, everything sold out completely. I remember it being 200 stacks @ 5g each, sold for 100g each.