consider using a messenger
Well I usually have books from abroad mailed to my office so that the office messenger can just go pick them up (my secretary gets the notice from the post office, since the notice is mailed to my office address because that's the mailing address I give the foreign book seller.) My secretary gives the messenger P50 to give to the post office guy and tapos.
If it's the messenger that goes to the post office - especially if he's used to going there for other things and he knows them and they know him (or even if not, basta he looks poor, frankly) - then the books get out easily. Don't want to get into the position of having to personally appear/be a target for more money.
Whatever works for you. Good luck.
I feel discomfort, therefore I exist.