It's not termed "raindrop", it's "airdrop" for your information. Well, we are on the same boat for that, they didn't clearly stated what are the conditions for this airdrop so it's expected we won't be able to tell if we're eligible or not...
There are clear criteria for awarding points for receiving airdrop, which are publicly available -
https://docs.arbitrum.foundation/airdrop-eligibility-distribution Similar criteria can be further used by other projects to calculate their airdrops in the future. Therefore, it is so important to know such criteria in order to be among the lucky recipients of airdrop in the future.
Well, I just hope that every participant who is entitled to receive their free tokens will enjoy them by selling them is a very reasonable price. Because it doesn't matter if they can get their reward if they can sell them and this usually happens to many airdrops, in fact, I was experiencing this before making me decide not to join this stuff again. However, I was positive that they will give what the people are expecting from them. Might not get listed to known exchanges but at least it was available to legit exchanges.