Is it safe to use a mini market money changer in kuta
I wouldn't even if they're honest rates are lower.
In Kuta there are many official money changers, use them. From what I've seen almost all the official money changers from Seminak down to Kuta have security guard(s) out front
Can you please say what you mean by "Mini market"? Do you mean convenience stores?
The place in Legian was called a mini market, just down from the Beachwalk mall.
If the Money Changer is PT.Central Kuta.
They will give you a receipt with your Rupiah, don't leave the counter until you have recounted/checked the amount of Rupiah is correct.
If you are close to Bemo Corner Kuta i'd recommend you change your money at PT. Dirgahayu Valuta Prima (it's green like Kermit the Frog) next to Bemo Corner coffee shop.
Basically the rule is if their sole business is changing money then they will be ok. Or ones located inside convenience stores. And the simple thing is, count the money, don't put it back down and be the last to touch it then you can never get ripped off