I'm posting here as a reference for the red trust I'm about to give
I think giving a neg to that guy would be completely appropriate. It's been a while, but I've had idiots sending me PMs begging for merits and I've negged them. Nobody's wanted to buy my account, though (lol).
As far as OP's situation goes, I probably would just report that post. That one is annoying, but IMO it doesn't rise to the level of deserving a negative feedback. Especially when a statement like that is only part of a post and not the entire post, it doesn't even qualify as "begging". Real begging could be seen in Meta right around the time when the merit system was introduced in January and again last month when the 1-merit Newbie rank-up requirement change happened.
Thankfully we don't see much more of this. It could be a lot worse than it is.