Legal Liability: This is the biggest risk. If your KYC ends up tied to something serious like money laundering or terrorism, authorities won’t hesitate to go after you. And since it’s your name on the account, you can’t simply deny it, you already submitted your documents.
And this is actually one of the scariest reason why such act should be totally disregarded, not minding how huge the offer may be for your KYC to be used by a third party. Because I'm actually happy people this days in the gambling community are now getting enlightened on the risk involved in lending their KYC or selling a KYC verified account to a total stranger for a fee, forgetting the risk involved, most especially the legal liability issue if the user happens to have used your KYC for fraud or illegal activity, as it's only the user whose name is on the KYC that will be charged and arrested, since he can't deny because of his KYC been used for the account verification.