Absolutely not, and the word " manipulated " cannot be true in the field of the merit system, but there are few traders of merit points (especially, some users who have an alternative account) who have been punished (through negative trust).
In addition to that, thanks to merit system, It has become easier to overthrow the scammers and to report them.
To cause considerable manipulation of merit system, a merit source needs to be involved in this. Since the admin is picking these merit sources, I am sure he is doing all the research about the chosen member. The post of merit source comes with a lot of responsibility. Also, I think that manipulation on large scale (awarding merit points in bulk) is very easy to notice. Since only established members are being chosen as merit sources, I do not think they will risk their account by getting into merit abuse (buying and selling of merit points) .