German here, we have the same thing (du vs. sie). Our rules may be slightly different than dutch but probably similar enough.
Police: definitely formal unless the officer is someone you know privately.
Shop: usually formal though some hobby-related shops (think GameStop or board games) might prefer informal.
Campsite: probably informal
As a general rule of thumb: informal is used with first names, formal is used with last names. Think about which name you would use in English and go with that. If in doubt, use the formal version or ask.
I have a wishlist that I share with my family and close friends. People follow that list unless they have an idea that they’re 100% sure about. I think the only times I got an unwanted gift was things I already had. Either because something went wrong coordinating between people (rare, everyone knows they can contact my partner to ask what’s still available) or because they accidentally bought the wrong thing (like the first book of a series instead the second one).
The only exception ever was during a single https://givin.gifts/ secret santa exchange where someone at the same time a) completely ignored my profile, b) gifted something below the stated minimum value, c) didn’t wrap my gift, d) didn’t include a card and e) didn’t include any packing material. They just threw a random 5€ item from the supermarket into an unpadded box and called it a day.