But even if the charity you pick only yields 1 euro of value from the 1000 you send, it’s still be better to send the money.
That’s up to your own personal utility function of course, but another option is to donate somewhere else instead. There are still a great many causes that can do a lot more good for a lot more people in similarly dire situations than getting €1 worth of help out of every €1000 to the people who need it.
Yes, this sucks for people who are in terrible situations where helping them is also orders of magnitude more inefficient and/or dangerous to those trying to help than others in similar need. Maybe it feels better to spend your €1000 to give €1 of help to someone in such a situation, than to give hundreds of times more help to people in situations elsewhere that are just as bad but more accessible.
This doesn’t look like a bet. It looks like a service for which you charge €3500 and 3+ months of the customer’s time, but will refund €2000 of that if they don’t think you lived up to your claims.