most want like 20 of them so will take you a bit to get your stock up. i dunno maybe 5 k ea. o.O that's 100k for 20 of them. you have to see what the most reward you can get from a bod then make it 50% of the reward or more, without them catching on. let's say organics are going for 120 ea and they can get 5k from a large bod. that's 600k they "could" bring in if they got the highest reward. so instead of charging them 300k say "i'll be nice i'll charge you 200k. white wyrms will cost 250k for 20, and drakes will cost you 100k for 20" without them realizing too much you just made 550k or most of their reward. hhehehe but most of the time they could get a +5 lore gear which is expensive. 700k-1 mil so really you point that out and now that 550k doesn't look so bad.
note when selling: rule of power "appeal to their self interests" and you'll win most of the time.
greed is always on the seller's side.