Thanks Werner, I understand everything you have mentioned.
I'm hoping you can clarify it even further though.
Lets say I buy 100k worth of BTC/ZAR from Luno, it costs 1% to do the transaction on Luno side, awesome, I now have 99k worth of BTC/ZAR
I now want to sell my 99k worth of BTC/ZAR 10 seconds later as an emergency or whatever came up. I sell everything ( not sure how much Luno asks, maybe R18.50 or a percentage again ) and I assume it costs another 1k max.
So in theory, I should get back roughly 98k in ZAR value since only 10 seconds passed since a bought it, right?
Unfortunately we know the answer is no, I'll probably get back maybe 80k if I'm lucky.