Change status of page after an event (Looking for best practice advice)

What you could do is create a metabox for the ‘People’ custom post type which would have radio values ‘Not Sponsored’ and ‘Sponsored’ (Not Sponsored b default). PayPal posts some transaction details to the notify url you have specified. Once you recieve the proper information from PayPal, like payment status is completed, then you could update the particular ‘People’ custom post’s sponsored meta info with ‘Sponsored’. To create metaboxes you could check this out -> Add “Post Options” for new wordpress post

Hope this helps.