Why don't you promote your account on
https://localcryptos.com/ or
https://localbitcoins.com/ instead of creating a site that looks like an exchange platform?
Also, going outside LBC escrow means that there is no guarantor other than your reputation, which is difficult to trust, especially if you want to make a transfer of huge sums.
So are you legally registered company in Cambodia?
I'm not a Cambodian but wonder if there are Cambodians here who can attest about the existence of your business.
I think they are middlemen just like LBC sellers and I don't think there is legislation in Cambodia that prohibits trading in cryptocurrencies.