How can we assure this
We are using our own methods to create&verify the accounts. We're always using whitelisted IPs, and we verify the account with REAL credit card not a Virtual or a Prepaid one.
We have packages, which are ID&address proof verified packages. On these accounts we send the documents to paypal before they even ask for it ( using their telephone&email support and our native speaking operator), so we "make them sure" that we're real persons, and not robots or fraudsters.
Mobile number verification
ALL of our sold accounts comes with verified mobile number. No matter if it's US&EU account, we will give you a way of receiving the SMS from paypal, so if in the future they need to verify your mobile number account, it will not cause any problem for you.
But I am not sure that your these steps yet will guarantee a bulletproof account with PayPal because I had experience of a complete genuine account got limited just with a reason of frequent highly volume transactions. To avoid problems with PayPal, the better solution must be quitting them, I did that long back itself.