Upvote:1
It is comprehensible that you like know your donation goes not in vain and the one accepting your donation is legitimate. This is because you like please that your donation goes well and effective so that you will multiply good Karma when you rethink and think about how it is well contributed. The most important thing here is you need to multiply your pleasant feeling by thinking again and agin when you did a good, legitimate donation.
So for donation, it is wise to choose people to whom you donate. If you cannot choose (are you doing donation on regular basic and difficult to examine/check at the point of time of donation?) try not have second thought, regret, disappointment after donation. At least, try to please by reviewing yourself that you got rid of attachment on things/money that you just donated. You should not linger your thoughts about quality of donee(s) which could do harm on your pleasantness of doing donation (difficult and challenging mind exercise for most people).
Metta
To inculcate Metta, you need to know it is opposite of aversion and hatred. Our Lord Buddha said many times that Metta is unmeasurable, limitless making up of your mind. So Metta is not correlated with quality/value/ethic/intention or any physical quality or moral status of any living being you are trying to spread on. It is not appropriate just spreading Metta to good people or people good to you. You can put Metta to any living great benefactor as well as living tyrant dictator. To achieve this you have to understand that no matter the target living being shall receive your Metta or not, you definitely have peace and pleasant mind without aversion and hatred by spreading Metta to infinite living beings around all directions (east, west, south, north, ++, up and down).
By spreading Metta to all living beings(unlimited), you should expect the following effects of it (need citation in Pali Canon).
Upvote:5
If funds are limited and the opportunities to donate are plenty, you should find out which is the best place to donate as in who is genuine, who will benefit the most, who is the most worthy etc. It's an aspect of wisdom which guides Metta to have the best possible outcome.
It's important to note the difference between worrying and looking for the best available option. The former is a consequence of clinging whereas the latter is a form of wisdom.
The Skandhas(5 aggregates) is a different teaching which has nothing to do with Metta, except for Metta bieing an instance of Sankhara-skandha(mental formations).
Metta can never be craving, but craving can disguise itself as Metta. Ex: Wanting to donate because the collection girl is pretty; wanting to join community service to get a chance to spend time with someone you are attracted to; wanting to donate to impress someone; wanting to donate to get a heavenly birth etc.
Technically speaking, wanting to help the poor & the afflicted is more Karuna(compassion) than Metta. Metta is simply kindness.