I'm a receipt checker due to being frequently overcharged, especially at the grocery store, so if I notice anything out of the ordinary I usually have it corrected right away. If they forgot to ring an item in my cart I definitely pay for it, if something is off by 20cents I probably won't notice.
My mom was a bank teller for years and was fired for having a drawer that didn't balance. Very traumatic in my childhood experience, so I always double count the money from the bank and return any overages. It's happened a few times.
Another board I frequent had a similar topic recently and one poster mentioned her mom bought a $299 sewing machine at target that rang through at 2.99. Her mother happily took it and didn't say a word.
In that situation I would not have been able to walk out of the store knowing that a huge error was made. However, I'm on another board where we seek out bargains and use coupons to our advantage to even make money sometimes. I don't see anything wrong with that.
When it comes to someone's personal money, I will do anything and everything to make sure they receive their lost belongings or are being paid the proper amount in an exchange of money. This comes from something I'm not proud of in my long ago past.
I was heading out for the weekend on a JW camping trip and had ZERO money for food and had no idea what I was going to do. Yes, I probably should have just stayed home, but as a young JW I was desperate for social contact. I went to public restroom in my apartment complex and found $37 on the sink. Crumpled up just like someone had been holding it in their hand, set it down to wash their hands and then forget the money.
I thought it was a sign from Jehovah that I should go on the trip and snatched up that money before I really even thought about it and went on my merry way. Eventually my conscience caught up with me and to this day it bothers me. I think about how sad and perhaps even desperate the person was that lost the money. I worry that it was a mom going to the store with the week's grocery money and they went hungry because of my greed and dishonesty. I have dozens of different scenarios that I torment myself with.
In a way, I'm grateful for the incident as it has shaped my dealings with people and money for the rest of my life. But I'm still mad at myself.