As I am one of those who contacted you, this may be interpreted as a conflict of interests. But at the expense of perhaps cutting my own throat, I'll answer.

There is no 'fair' way. Look at the variables, is it going to be flipped?, do they already have a number of them?, do they have a car?, is it running?, do they have more than one car?, how do you tell if someone is telling you the truth or just blowing smoke?

If you don't have personal knowledge of the person, the answer to all of these is that you wouldn't know the answer until after the deal is done. And it might not go the way you intended it to.

It is noble to help the hobby and those in it. There are few people that would pass up a chance for profit to do so. But again, at the expense of perhaps cutting my own throat, if it were me I would retract my offer and keep the filters. Which is better? 75 people disappointed that they didn't get one or 73 people PO'd that someone else was chosen to be more deserving than them?

Just my You asked for my opinion and you have it.