This is very much worth knowing about and understanding.
Basically, bank details can only be used to send you money except for the specific case of Direct Debits where they are used to claim money owed.
This is why the Direct Debit Guarantee exists, as it allows you (as a consumer) to claim money back if this facility if abused by a retailer or used fraudulently.
Next time you want someone to send you money, or you want to send them money, you could use Monzo’s Monzo.me feature instead. This doesn’t use account details and works even if the other person isn’t using Monzo, so it is good for occasions where you don’t entirely trust them to have your bank details.