How do Ecto's work?

Okay, i'm j/w how this works, i hear ppl sell them for around 6.5p, in the shop there worth around 7.5p....On the auctions it say's = merchant - 1 ecto = 1p
I don't quiet understand, say if i want to buy a weapon that costs 200p, and i have 100p how would i transfer the other 100k (using ecto's), as that's the way people do it??

if they say ecto price = -1k merchant and the merchant sells it for 7.5k then the ecto price each is 6.5k.

So 100k in ectos would be around 15 ectos. Hope you understand :P

People won't sell'm to the trader coz that'll drop the price. Right?

That too but people almost always get better price from other players than from traders.