Luno is a trusted exchange [...]
I guess
trusted is a relative term.
I wouldn't trust that exchange at all. No reason to use an unknown exchange with low trading volume and unknown security measurements if you can use way better exchanges.
I used their exchange once to sell small amount of Bitcoin since they support my local currency and bank. The volume is low, but i don't experience any problem.
Since i only used it once, i wouldn't recommend it due to low volume and i've no idea how secure is their exchange, but i'm sure it's not plain scam.