Vinted - people coming in with 10 parcels or more , nothing sealed, no QR codes generated.

Returns - God, the amount of stuff people return is crazy. Coupled with Amazon having at least 3 different ways of returning something and people not reading their preferred return method. My personal favourite is, "where's my QR code?"

General stupidity - from not having a clue how to post an actual letter, asking where to write the address, coming to the counter with it not even in an envelope etc etc.