1. The site only provides you verified scripts which are already published in Tradingview. You may ask the owner/publisher of the scripts in Tradingview which are linked from this store to verify authenticity in case of doubts if any.
Selling premium scripts subscription outside TradingView is completely legal.
Authors can manage who can access their indicators. This is great for commercial vendors, or authors who want to protect their IP, or share with only a few select people - the reasons could be many. If someone wishes to sell indicators, the author may charge off-site for them, and then provide access to the paying customers.
Simply choose the "Invite-only script" option when publishing, and only users who you specifically add will be able to use it.
2. Your payments are securely processed through Paypal Gateway and not through this site. So, all payments are highly secured and have supports of excellent service by PayPal.