I guess I would tell the Mom that the collection is worth more than she believes and make her a better offer that would still allow you to make a reasonable profit. Then I'd take 10% of that profit and donate it to some worthy cause in the kid's name. I'd then inform the parents anonymously of the donation made on their child's behalf. That way you could still make some money, you'd have done a good thing, and you'd sleep better at night.
