Indeed it is annoying, there should be a small tab instead of a whole new window to send merits.

"Merit" are used to rate the post according to the efforts of user, this will be quite unfair if you want to keep a good, very good and excellent post on the same level.
It will not reduce fake-merit exchange, however it will decrease the impact of merit system on the forum.
Merit system is useless if it will be treated as "Like" button.