Th fastest toon to sell are those with things that are neccesary, but dosn't increase price.
for example:
Mage Lv.80, dual talents, 280% flying mount, tailoring + Engineering at 450, 5k gold to buy starting gear. Sell it naked for 30 coins.
Instant lvl 80 doesn't include thos things, and currnt gold value is lik 1.5k -> 1 coins. getting proffs + flying + starting gold givs lots of value on toon. (that 1.5k gold -> 1 coin is just example, i dont rally know the current value cuz im drunk and tird to check it while writing.).
Also anothr thing: it's way easier to sell naked toon wth proffs and flying mount+dual talent spec, than som geared toons.