It's up to you how you spend your Merits and when you think he deserves 20 it's absolutely no problem to do so.
The only way of Merit abuse needs to have a really clear pattern for giving huge amounts of Merit to shitposts or send a Merit to your own alt. As long as the post of cryptobaro isn't a bounty submission I'm totally ok with your intention to spend your sMerit.
But finally i was granted with many more and i find it is unfair that they all were send to me, because he also helped me beginning this anti-scammer journey!
That's how the Merit system works, you can't defend yourself against receiving Merit.