my simple guide is this

mass buying is an effective, but risky way to make/lose lots of tc
only misc buying at low starting tc is bad
buying textures in sets make better, and quicker profit than single textures
all colors are good colors
the higher price the item, the less lee-way you go on haggling
never "meet in the middle", if someone wants to meet in the middle, that extra 1-5k won't kill them so raise your offer in very small, but reasonable increments
never competitive over-bid (eg, someone you don't like beats your offer, don't offer more if you know profit is small, or not there)
never sell too quick, be mindful that your tc isn't gone and trading items is sometimes available

cake your tut is pretty okay but you go into specifics too much
you just need basic rules