kraxxykats:
I'll assume your post about keeping the unexpected overcharge is in jest. In case it isn't a joke...
It's not a good idea to keep the overcharge. It's greedy, unethical and an indication of a lack of character and good customer service. It could also get you a negative feedback if the buyer figures out that he/she was overcharged on shipping (some buyers do check out their shipping charges for seller honesty).
Good sellers don't keep overcharges on shipping - they refund the overcharge and keep their reputation, conscience, and self-respect intact, which results in a better and more successful buyer and seller experience.
When a customer sees that you DO refund for an overcharge, it increases the likelihood that you will be receiving a positive feedback, and you've just greatly improved the likelihood of repeat business from this customer. This has happened to me on several occasions, because I am always honest in refunding a shipping overcharge on what I thought would only be a single one-off order from a buyer. Instead, they thanked me for the shipping overcharge refund and ordered more.
This type of refund engenders TRUST between buyer and seller, and that is the difference between a successful seller and one who shows greed and lack of trustworthiness, often getting caught and not ordered from again by a smart buyer.
Cheers, Duffy