What is line between a donation and boosting?

I have been offered 3b in skins, 1b in skins, 200m in coins, 50m, ext. I have a 5b nw but I still decline every time because I don’t want to get banned for boosting or duping.

The rule is basically: “One time transfers are not bannable, unless it is a large amount of money”

What is actually considered a donation vs boosting?