More than likey they are buying the psn vouchers on stolen credit cards from online shops like cdkeys.com then using the codes to purchase games on new accounts from us store, which is lot cheaper than the psn for uk. I used my us account to buy Batman from us store for 38 quid instead of 55 quid on the uk store.
As they are puchasing the games legally and selling it on, i doublt the account will be stopped, just means you will need to have lots of accounts stored on you ps4 to play the games under your account. I thnk the limt of accounts on the ps4 is 16 seperate user accounts.