I think that people can start to justify things to themselves like using the company / party credit card with the logic of martyrdom, especially the political class who are so used to claiming expenses.
'I was taking political phone calls all evening and then I emailed wee Mhairi so I'm entitled to call it work and order a fish supper on the nat plastic', and it soons turns into 'I haven't had time to go proper shopping because I was shouting into a zoom camera about party discipline so I'll just order myself some stuff I need to decompress, a bit of gardening would be nice maybe and some Scottish lobster'.
Everybody needs a line manager or senior civil servant going though this stuff once every month to check for people going 'off piste' - it's standard practice. Otherwise, well, expenses scandals happen.