Agree, several I could list. But special shout out to
penhead. I sold him something - a beholder shield maybe - and ever since that deal, he's been giving me free books of range. Can't beat that! I owe him a bunch of books of power.
Honorable mentions:
Sintoque - never interacted in game, but totally respect the efforts to rid the game of "spotting".
VariusAvus
gameplayerdude
itblobboy - if he still exists...
M668 - always buys my items for good prices, as I am not yet blessed to have 60% resale